In a dbgutil build LO aborts on an assertion failure the moment
KFileDialog is open. It's definitely on okay to release SolarMutex just
like that, since the Qt event loop is integrated with LO's, it'll call
back to LO code without the mutex held.

This reverts commit 13a34f4c.

Conflicts:
	vcl/unx/kde4/KDE4FilePicker.cxx
	vcl/unx/kde4/KDEXLib.cxx

Change-Id: Idfa27fbb4728b529c37c25f710ea208fdaa4455c