Running Tux Paint under macOS in Korean mode (and some other languages) causes
it to crash, unless "load system fonts" option is also enabled. Some
investigation showed the issue occurs when num_font_families is 0 in fonts.c.
This change removes the assumption from the code that assumes num_font_families
has at least one record.
Previously, the DMG's default window is slightly larger than the
background, exposing some whitespace. This fixes the window size to be
identical to the background image, so no whitespace is exposed.
Previously `make install` on macOS created TuxPaint.dmg, but it was a
simple disk image.
Now TuxPaint.dmg is formatted as one would expect from any other macOS app,
with a Tux folder icon, symlink to the /Applications folder, and a
background image with an arrow.
