QFontCache crash when DLL is unloaded

When main app loads a DLL that uses a new font (a font that the main app does not use) and that DLL is unloaded then main app will crash when it is being closed.

See attached files for an example (compile mainDll.cpp as a DLL and qfontcache_crash.h/cpp as an EXE):

• start EXE
• press load button
  >> a new widget with the text "test" will be added
• press unload
  >> the new widget is removed and everything is cleaned up
• close the app
• a crash will occur

Location of crash:
qfont.cpp (line 2748) at command "engineDataCache.clear();"

Qt 4.8 does not have this issue.