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.h

@@ -79,8 +79,8 @@ public:
 
         for (int i = from; i < to; ++i) {
             const Use use = future.resultAt(i);
-            if (! use.line)
-                continue; // skip it, it's an invalid use.
+            if (use.isInvalid())
+                continue;
 
             const int blockNumber = use.line - 1;
             chunks[blockNumber].append(use);