[0.4.9][SHELL32] Fix uninitialized variable usage. CORE-15251 (#3986)

[0.4.9][SHELL32] Fix uninitialized variable usage. CORE-15251 (#3986)

This fixes log spam about NM_CUSTOMDRAW not being handled,
e.g. when interacting with the start-menu or filebrowsers menubar.
Less logging implies faster painting here with dbg-builds.

fix picked from commit 0.4.15-dev-3229-g 22e58e68aa35a1ba49d280b12f99f7f03f5f8633

The bug was a regression of 0.4.9-dev-151-g 0aed0fd167863d1674e73a7fdb22fd1fb7a319f0 very likely,
The symptom with the logging can neither be observed in unpatched releases/0.4.8 nor in releases/0.4.7