BuildSystem: Fix font list

We want to add the individual strings to the list
and not add a list object to the list.

Without this patch, sorting failed because "str < list"
is not a valid operation in python.

editor/SCsub

@@ -76,7 +76,7 @@ if env['tools']:
 
     # Fonts
     flist = glob.glob(path + "/../thirdparty/fonts/*.ttf")
-    flist.append(glob.glob(path + "/../thirdparty/fonts/*.otf"))
+    flist.extend(glob.glob(path + "/../thirdparty/fonts/*.otf"))
     env.Depends('#editor/builtin_fonts.gen.h', flist)
     env.CommandNoCache('#editor/builtin_fonts.gen.h', flist, run_in_subprocess(editor_builders.make_fonts_header))