Fix Coverity uninitialized member warning

nyalldawson · nyalldawson · commit f1249cee7dba · 2018-04-06T14:19:09.000+10:00
(cherry-picked from 25a9929)
diff --git a/src/core/qgsaction.h b/src/core/qgsaction.h
@@ -251,7 +251,7 @@ class CORE_EXPORT QgsAction
     mutable std::shared_ptr<QAction> mAction;
     QUuid mId;
     QgsExpressionContextScope mExpressionContextScope;
-    bool mIsEnabledOnlyWhenEditable;
+    bool mIsEnabledOnlyWhenEditable = false;
 };
 
 Q_DECLARE_METATYPE( QgsAction )
