[commands] Correct concurrency never releasing during prepare call

discord/ext/commands/core.py

@@ -781,6 +781,7 @@ class Command(_BaseCommand):
         if self._max_concurrency is not None:
             await self._max_concurrency.acquire(ctx)
 
+        try:
             if self.cooldown_after_parsing:
                 await self._parse_arguments(ctx)
                 self._prepare_cooldowns(ctx)
@@ -789,6 +790,10 @@ class Command(_BaseCommand):
                 await self._parse_arguments(ctx)
 
             await self.call_before_hooks(ctx)
+        except:
+            if self._max_concurrency is not None:
+                await self._max_concurrency.release(ctx)
+            raise
 
     def is_on_cooldown(self, ctx):
         """Checks whether the command is currently on cooldown.