pow-migration: Fix detection of switching validator in pre-stake

Fix the detection of switching validator in pre-stake as it was
filtering always transactions that didn't have the minimum stake but
for switching to another validator in pre-stake, the stake is already
above the minimum since it was already counted to another validator.

This fixes #2399.

pow-migration/src/state/mod.rs

@@ -1,6 +1,11 @@
 pub mod types;
 
-use std::{collections::HashMap, ops::Range, str::FromStr, vec};
+use std::{
+    collections::{hash_map::Entry, HashMap},
+    ops::Range,
+    str::FromStr,
+    vec,
+};
 
 use nimiq_bls::PublicKey as BlsPublicKey;
 use nimiq_genesis_builder::config::{
@@ -392,27 +397,38 @@ pub async fn get_stakers(
                                 log::info!(staker_address=txn.from_address, validator_address=%address, "Found pre-stake transaction for validator");
                                 if let Ok(staker_address) = Address::from_str(&txn.from_address) {
                                     let stake = Coin::from_u64_unchecked(txn.value);
-                                    if stake >= Coin::from_u64_unchecked(Policy::MINIMUM_STAKE) {
-                                        validator.total_stake += stake;
-                                        stakers
-                                            .entry(staker_address.clone())
-                                            .and_modify(|staker| {
-                                                // If we have an entry for this staker, treat this as a switch to another
-                                                // validator or an increase of the stake (if the validator isn't changed)
-                                                staker.delegation =
-                                                    validator.validator.validator_address.clone();
-                                                staker.balance += stake;
-                                            })
-                                            .or_insert(GenesisStaker {
-                                                staker_address,
-                                                balance: stake,
-                                                delegation: validator
-                                                    .validator
-                                                    .validator_address
-                                                    .clone(),
-                                                inactive_balance: Coin::ZERO,
-                                                inactive_from: None,
-                                            });
+                                    match stakers.entry(staker_address.clone()) {
+                                        Entry::Occupied(mut entry) => {
+                                            // If we have an entry for this staker, treat this as a switch to another
+                                            // validator or an increase of the stake (if the validator isn't changed)
+                                            let staker = entry.get_mut();
+                                            staker.delegation =
+                                                validator.validator.validator_address.clone();
+                                            staker.balance += stake;
+
+                                            // Update the validator total stake
+                                            validator.total_stake += stake;
+                                        }
+                                        Entry::Vacant(entry) => {
+                                            // If there wasn't a staker registered for this address, check minimum stake
+                                            if stake
+                                                >= Coin::from_u64_unchecked(Policy::MINIMUM_STAKE)
+                                            {
+                                                entry.insert(GenesisStaker {
+                                                    staker_address,
+                                                    balance: stake,
+                                                    delegation: validator
+                                                        .validator
+                                                        .validator_address
+                                                        .clone(),
+                                                    inactive_balance: Coin::ZERO,
+                                                    inactive_from: None,
+                                                });
+
+                                                // Update the validator total stake
+                                                validator.total_stake += stake;
+                                            }
+                                        }
                                     }
                                 } else {
                                     log::error!(