ClangRefactoring: Don't update the database if something went wrong

We can get an compile error. In that case we should not update the
database. In the future we should have a mechanism to report about the
database state.

Task-number: QTCREATORBUG-21949
Change-Id: I203346d536b007171f7bf255047409431c44a85a
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/tools/clangrefactoringbackend/source/symbolscollector.h

@@ -52,7 +52,7 @@ public:
 
     void clear() override;
 
-    void collectSymbols() override;
+    bool collectSymbols() override;
 
     void doInMainThreadAfterFinished() override;