patch 8.1.0121: crash when using ballooneval related to 'vartabstop'

Problem:    Crash when using ballooneval related to 'vartabstop'.
Solution:   Initialize balloonEval->vts to NULL. (Markus Braun)
diff --git a/src/gui_beval.c b/src/gui_beval.c
index 7e46250..49694cf 100644
--- a/src/gui_beval.c
+++ b/src/gui_beval.c
@@ -111,28 +111,19 @@
 	return NULL;
     }
 
-    beval = (BalloonEval *)alloc(sizeof(BalloonEval));
+    beval = (BalloonEval *)alloc_clear(sizeof(BalloonEval));
     if (beval != NULL)
     {
 #ifdef FEAT_GUI_GTK
 	beval->target = GTK_WIDGET(target);
-	beval->balloonShell = NULL;
-	beval->timerID = 0;
 #else
 	beval->target = (Widget)target;
-	beval->balloonShell = NULL;
-	beval->timerID = (XtIntervalId)NULL;
 	beval->appContext = XtWidgetToApplicationContext((Widget)target);
 #endif
 	beval->showState = ShS_NEUTRAL;
-	beval->x = 0;
-	beval->y = 0;
 	beval->msg = mesg;
 	beval->msgCB = mesgCB;
 	beval->clientData = clientData;
-#ifdef FEAT_VARTABS
-	beval->vts = NULL;
-#endif
 
 	/*
 	 * Set up event handler which will keep its eyes on the pointer,