cogl/onscreen: Add missing error untrap calls
Every mtk_x11_error_trap_push() must be paired
with an mtk_x11_error_trap_pop[_with_return]() call
otherwise all future errors will be caught and ignored
even if they shouldn't be.
Every mtk_x11_error_trap_push() must be paired
with an mtk_x11_error_trap_pop[_with_return]() call
otherwise all future errors will be caught and ignored
even if they shouldn't be.