Editor: Add further Use::isInvalid() guards

Task-number: QTCREATORBUG-8738

Change-Id: I297731f15bd9001f7edc83c956a15ef660929dc7
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cppchecksymbols.cpp

@@ -1104,7 +1104,7 @@ static const int chunkSize = 50;
 
 void CheckSymbols::addUse(const Use &use)
 {
-    if (!use.line)
+    if (use.isInvalid())
         return;
 
     if (! enclosingFunctionDefinition()) {