[3.4-dev] Minor bugs with Win client

[PowerWyrm]

1) term_force_font
This is called twice: in term_change_font and init_windows. The first time, it correctly sets defaut tile width/height with font width/height, but sets "bizarre" flag incorrectly (should be set only if font has been forced to default). The second time, it uses hardcoded values of 8 and 13, which is incorrect since the default font is now 8x12.
Fix: make a static function and call that twice to avoid the error (and this removes duplicate code at the same time)

2) New default layout (since 15/04)
The new default layout uses string_make for default fonts. However, the default fonts have already been allocated in load_prefs_aux, leading to some memory leaks.
Fix: call string_free in default_layout_win before calls to string_make