Update Telegram.php

Added check NULL update object when execute command without update using $telegram->executeCommand('command') function. This would prevent fatal error caused coming from NULL object used as an argument in setUpdate() method.

src/Telegram.php

@@ -682,7 +682,11 @@ public function executeCommand(string $command): ServerResponse
         } else {
             //execute() method is executed after preExecute()
             //This is to prevent executing a DB query without a valid connection
-            $this->last_command_response = $command_obj->setUpdate($this->update)->preExecute();
+            if ($this->update) {
+                $this->last_command_response = $command_obj->setUpdate($this->update)->preExecute();
+            } else {
+                $this->last_command_response = $command_obj->preExecute();
+            }
         }
 
         return $this->last_command_response;