Delete lib from sys.modules when an exception happens during load

Author: Kuro-Rui

redbot/core/bot.py

@@ -1630,15 +1630,20 @@ async def load_extension(self, spec: ModuleSpec):
 
         lib = module_from_spec(spec)
         sys.modules[name] = lib
-        spec.loader.exec_module(lib)
+        try:
+            spec.loader.exec_module(lib)
+        except Exception:
+            del sys.modules[name]
+            raise
 
         if not hasattr(lib, "setup"):
             del lib
             raise discord.ClientException(f"extension {name} does not have a setup function")
 
         try:
             await lib.setup(self)
-        except Exception as e:
+        except Exception:
+            del sys.modules[name]
             await self._remove_module_references(lib.__name__)
             await self._call_module_finalizers(lib, name)
             raise