Fix Exception #478
Description
Steps to Reproduce
════════ Exception caught by widgets library ═══════════════════════════════════
The following LateError was thrown while finalizing the widget tree:
LateInitializationError: Field '_exerciseNameController@85120925' has not been initialized.
When the exception was thrown, this was the stack:
#0 _ExercisesScreenState._exerciseNameController (package:wger/screens/exercises_screen.dart)