patch 8.0.1296: checking the same condition twice

Problem:    Checking the same condition twice. (John Marriott)
Solution:   Check blinkwait.
diff --git a/src/gui.c b/src/gui.c
index e6cc544..7ef1c95 100644
--- a/src/gui.c
+++ b/src/gui.c
@@ -1118,7 +1118,8 @@
 	gui_mch_set_blinking(shape->blinkwait,
 			     shape->blinkon,
 			     shape->blinkoff);
-	if (shape->blinkoff == 0 || shape->blinkon == 0 || shape->blinkoff == 0)
+	if (shape->blinkwait == 0 || shape->blinkon == 0
+						       || shape->blinkoff == 0)
 	    gui_mch_stop_blink();
 #ifdef FEAT_TERMINAL
 	if (shape_bg != INVALCOLOR)