patch 8.2.3756: might crash when callback is not valid Commit: https://github.com/vim/vim/commit/4dc24eb5adbcc76838fae1e900936dd230209d96 Author: Yegappan Lakshmanan <yegappan@yahoo.com> Date: Tue Dec 7 12:23:57 2021 +0000 patch 8.2.3756: might crash when callback is not valid Problem: might crash when callback is not valid. Solution: Check for valid callback. (Yegappan Lakshmanan, closes https://github.com/vim/vim/issues/9293)

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