Correctly parse offset from info proc mappings output (hugsy#1096)

Fix the Offset column in the `vmmap` command by getting the offset
from the correct column in `parse_gdb_info_proc_maps`.

gef.py

@@ -10705,7 +10705,7 @@ def parse_gdb_info_proc_maps(cls) -> Generator[Section, None, None]:
                 break
 
             parts = [x.strip() for x in line.split()]
-            addr_start, addr_end, offset = [int(x, 16) for x in parts[0:3]]
+            addr_start, addr_end, _, offset = [int(x, 16) for x in parts[0:4]]
             if mock_permission:
                 perm = Permission(7)
                 path = " ".join(parts[4:]) if len(parts) >= 4 else ""