Fix index out of range crash

Change-Id: Ifa943d3d240c7ffab0bd21f50ff66d796c78401e
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/qmldesigner/designercore/metainfo/subcomponentmanager.cpp

@@ -101,7 +101,7 @@ bool SubComponentManager::addImport(const Import &import, int index)
     }
 
     if (importExists) {
-        if (index == -1)
+        if (index == -1  || index > m_imports.size())
             m_imports.append(import);
         else
             m_imports.insert(index, import);