Fix bug #7099: Math toolbars don't autoshow.

Fix bug #7099: Math toolbars don't autoshow.

In GuiApplication::readUIFile() the settings for views gets removed if the ui file is newer than the saved timestamp in the settings. Later the non existing settings will be used to initialize the visibility. The default value for a non existing setting is 0. The visibility_ variable does never get changed afterwards. And therefore
we will again write 0 to the registry.

We should have read the ui file instead when we can't find the registry value.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@37075 a592a061-630c-0410-9148-cb99ea01b6c8