Avoid warning on empty expressions

For some reason, Q_UNUSED includes already a semicolon, adding one
on the user side creates an additional empty statement.

Change-Id: I9c5e8fac381345a60792cb75e2938fd53958d3b0
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/modeleditor/modeldocument.cpp

@@ -69,7 +69,7 @@ ModelDocument::~ModelDocument()
 Core::IDocument::OpenResult ModelDocument::open(QString *errorString, const QString &fileName,
                                                 const QString &realFileName)
 {
-    Q_UNUSED(fileName);
+    Q_UNUSED(fileName)
 
     OpenResult result = load(errorString, realFileName);
     return result;