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/texteditor/codeassist/assistproposalitem.cpp

@@ -122,7 +122,7 @@ bool AssistProposalItem::implicitlyApplies() const
 
 bool AssistProposalItem::prematurelyApplies(const QChar &c) const
 {
-    Q_UNUSED(c);
+    Q_UNUSED(c)
     return false;
 }