The current version of the code incorrectly assumes that the lpszClass
member of CREATESTRUCT passed with WM_CREATE will point to the same
memory used for the CreateWindowEx class name parameter, and uses a
pointer comparison to check for class name equality.
As a side effect of commit e41c255be6ba66d1eec7affe674b8cc7699226b8
"win32u: Use send_message_timeout for WM_CREATE and WM_NCCREATE" the
CREATESTRUCT lpszClass member started pointing to different memory,
breaking the current implementation of MCIWND_Create().
This commit fixes the problem by performing a proper, case-insensitive
string comparison to determine class name equality.
Wine-bug: https://bugs.winehq.org/show_bug.cgi?id=53578
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v3: msvfw32: Use string comparison to determine class name equality.
https://gitlab.winehq.org/wine/wine/-/merge_requests/726