WINGs/wfont.c: Avoid returning font=NULL in WMCreateFont()

WINGs/wfont.c: Avoid returning font=NULL in WMCreateFont()

WPrefs tries to use the fonts listed in the WMCreateFont() call (from WPrefs.c),

font = WMCreateFont(scr, "Lucida Sans,URW Gothic L,Times New Roman,serif"
                         ":bold:pixelsize=26:antialias=true");

and 'font' is later used without accounting the possibility of it being NULL in

WMSetLabelFont(WPrefs.nameL, font);
WMReleaseFont(font);

In particular, WMReleaseFont(font) will kill WPrefs ungracefully with the
following message if font=NULL

WPrefs: wfont.c:193: WMReleaseFont: Assertion `font!=((void *)0)' failed.
Aborted

That happens because the return value of WMCreateFont() can be NULL, so this
patch makes WMCreateFont() never return NULL. If the font creation fails for
some reason (see below), we try to use the emergency DEFAULT_FONT and print
debugging information telling what's going on. If the use of DEFAULT_FONT
also fails, then we terminate WPrefs with exit(1) and let the user know
why exactly if failed.

This bug happened because the font "Lucida Sans" (the first possibility
in the initial call to WMCreateFont()) "exists" in my system as a stale
symbolic link to a location which no longer exists after an upgrade from
java from 1.5.0.14 to 1.5.0.15

    /etc/alternatives/LucidaSansDemiBold.ttf ->
    /usr/lib/jvm/java-1.5.0-sun-1.5.0.14/jre/lib/fonts/LucidaSansDemiBold.ttf

So the call to XftFontOpenName(display, scrPtr->screen, fname) with
"Lucida Sans" being the first possibility for Xft to try out ended up in 'font'
being NULL because, as far as the Xft library was concerned, "Lucida Sans"
produced a positive match (due to it existing as a symbolic link) but in the end
a NULL result was produced due to the missing symbolic link destination. This later
exposed the bug of WMCreateFont() returning font=NULL and WPrefs.c not checking
whether font=NULL before using it. Bang!

If "Lucida Sans" was the _second_ entry to try and the first one had suceeded,
this bug would not have surfaced.

This solves https://qa.mandriva.com/show_bug.cgi?id=39677

Signed-off-by: Carlos R. Mafra <crmafra@ift.unesp.br>