CppEditor: Fix race condition for highlighting of local usages

Starting a renaming action involves looking up local usages. In this
case, a different code path than normal updates the editor's extra
selections, in order to make sure that the occurrence to be edited is
rendered in a special way. We must therefore prevent the normal handler
from taking action, as it would overwrite abovementioned special
selection.

Change-Id: Ia811b49b3023a0a366a43a69cc01e6b2b370acb5
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cppeditor/cppeditorwidget.cpp

@@ -805,6 +805,11 @@ bool CppEditorWidget::isSemanticInfoValid() const
     return isSemanticInfoValidExceptLocalUses() && d->m_lastSemanticInfo.localUsesUpdated;
 }
 
+bool CppEditorWidget::isRenaming() const
+{
+    return d->m_localRenaming.isActive();
+}
+
 SemanticInfo CppEditorWidget::semanticInfo() const
 {
     return d->m_lastSemanticInfo;