Fix class attribute dump_filename in ProfilerDebugPanel (#294)

We need `dump_filename` in `ProfilerDebugPanel` always initialised to avoid `AttributeError`

Fix #286

Author: kartikeyporwal

src/flask_debugtoolbar/panels/profiler.py

@@ -36,6 +36,8 @@ def __init__(
     ) -> None:
         super().__init__(jinja_env, context=context)
 
+        self.dump_filename = None
+
         if current_app.config.get("DEBUG_TB_PROFILER_ENABLED"):
             self.is_active = True
             self.dump_filename = current_app.config.get(