QComboBox: not accept wheel events for changing values

It is dangerous for combo boxes within scroll views especially.

Fixes: QTCREATORBUG-28103
Change-Id: Ibed498658ce9d6f5b90f6d7e8ec7c4f2bbd015aa
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/coreplugin/manhattanstyle.cpp

@@ -390,6 +390,10 @@ int ManhattanStyle::styleHint(StyleHint hint, const QStyleOption *option, const
         if (widget && widget->inherits("QTreeView"))
             ret = 0;
         break;
+    case QStyle::SH_ComboBox_AllowWheelScrolling:
+        // Turn this off completely to prevent accidental current index change on a scroll view
+        ret = false;
+        break;
     default:
         break;
     }