ux(dashboard): fix for dropzone width when resizing another panel

public/app/features/dashboard/row/row_model.ts

@@ -44,11 +44,11 @@ export class DashboardRow {
     }
   }
 
-  panelSpanChanged() {
+  panelSpanChanged(alwaysSendEvent?) {
     var oldSpan = this.span;
     this.updateRowSpan();
 
-    if (oldSpan !== this.span) {
+    if (alwaysSendEvent || oldSpan !== this.span) {
       this.events.emit('span-changed');
     }
   }

public/app/features/panel/panel_directive.ts

@@ -191,7 +191,7 @@ module.directive('panelResizer', function($rootScope) {
           }
         }
 
-        ctrl.row.panelSpanChanged();
+        ctrl.row.panelSpanChanged(true);
 
         scope.$apply(function() {
           ctrl.render();