PR Summary

Previously, if a figure number was not in the list of managed figures, the destroy would be skipped, but now that only happens if a figure number is passed. If a figure manager is passed, then the destroy happens regardless. In nbAgg, this loops around closing/close_event and eventually calls destroy again, leading to a RecursionError.

This broke in 9e6f112; cc @anntzer.

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• [N/A] New features are documented, with examples if plot related
• [N/A] Documentation is sphinx and numpydoc compliant
• [N/A] Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• [N/A] Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way