UI: Corrected Scaling of AREAMINX

Minimum horizontal area size should be scaled by UI resolution.

See D15865 for more details.

Differential Revision: https://developer.blender.org/D15865

Reviewed by Brecht Van Lommel

source/blender/editors/space_buttons/space_buttons.c

@@ -978,8 +978,7 @@ void ED_spacetype_buttons(void)
   /* regions: navigation bar */
   art = MEM_callocN(sizeof(ARegionType), "spacetype nav buttons region");
   art->regionid = RGN_TYPE_NAV_BAR;
-  art->prefsizex = AREAMINX - 3; /* XXX Works and looks best,
-                                  * should we update AREAMINX accordingly? */
+  art->prefsizex = AREAMINX;
   art->keymapflag = ED_KEYMAP_UI | ED_KEYMAP_FRAMES | ED_KEYMAP_NAVBAR;
   art->init = buttons_navigation_bar_region_init;
   art->draw = buttons_navigation_bar_region_draw;