pImplSVData->maGDIData.mnAppFontX is *not* a flag to determine if
application font dimensions should be reset. The way it currently works
is:

1. Application::SetSettings() is called to reset Window settings,
etc.

2. Settings are updated on all windows - but at the same time
pImplSVData->maGDIData.mnAppFontX is set to zero as a way of indicating
to the global function ImplCalMapResolution that we need to get the font
from the first window, or if this isn't available then create a new dummy
WorkWindow and use this to get the font data, and set the application
font to this.

This is very odd. What we really should be doing is calling on
ImplInitAppFontData directly from within SetSettings() instead of making
ImplCalcMapResolution detect that mnAppFontX is zero and there is a
valid first frame window.

Ultimately, this was found when I commited f76026a4 to move
ImplInitAppFontData from Window to Application. Somehow I entirely missed
that the font and style dropdowns in writer died, and I also somehow
a whole bunch of tests failed but I again didn't notice this either. With
this fix, I should be able to recommit the previous change.

Change-Id: Ib526954962fdc397fb3ddd3c21ae947d939db9e5