Regression: Unexpected condition in EDIT_UnlockBuffer when editing explore.exe with Notepad

reactos-livecd-0.4.15-dev-5647-gb6aaf5e-x86-gcc-lin-dbg
reactos-livecd-0.4.15-dev-5648-g0a851ea-x86-gcc-lin-dbg

Guilty commit : 0a851ea by katayama_hirofumi_mz 

• Open Notepad
• Edit explorer.exe

Opens fine but log an Unexpected condition in EDIT_UnlockBuffer requested to be reported.

err:(dll/win32/comctl32/edit.c:1245) es->text == 0 ... please report 

See : https://git.reactos.org/?p=reactos.git;a=blob;f=dll/win32/comctl32/edit.c#l1228

Also happens in CORE-19898

Wine 10.5 is affected in the same way: https://bugs.winehq.org/show_bug.cgi?id=58095

Problem does NOT occur in Wine using Wine's notepad BUT only if using ReactOS notepad.