Change Details

** Why ** This ensures that vtterm_cnungrab() is the mirror of vtterm_cngrab(). And the latter always call vt_window_switch() and thus the backend's vd_postswitch(). This makes sure that whatever the backend did during vtterm_cngrab(), it can undo it during vtterm_cnungrab().

**Why** This ensures that vtterm_cnungrab() is the mirror of vtterm_cngrab(). And the latter always call vt_window_switch() and thus the backend's vd_postswitch(). This makes sure that whatever the backend did during vtterm_cngrab(), it can undo it during vtterm_cnungrab().

** Why ****Why** This ensures that vtterm_cnungrab() is the mirror of vtterm_cngrab(). And the latter always call vt_window_switch() and thus the backend's vd_postswitch(). This makes sure that whatever the backend did during vtterm_cngrab(), it can undo it during vtterm_cnungrab().