When font loading is finished, restore the font list in the
corresponding async completion callback, and not in the
"notify::empty" signal handler of the fonts async set
This solves a problem arising when gimp_fonts_wait() is called
*inside* a "notify::empty" signal handler, emitted when reloading
fonts (causing the "empty" property of the fonts async set to
switch from TRUE to FALSE): When the wait is over, "empty" will
switch back from FALSE to TRUE, however, since the "notify" signal
is non-recursive, the corresponding handler will not be called,
gimp_fonts_wait() will return *before* the font list is restored,
and the caller will see an empty font list. This can happen under
certain circumstances when reloading fonts while the text tool is
active.
(cherry picked from commit 0e19f159f5)
7c72d8cfa1