Mark forward template class declarations.

src/plugins/cppeditor/cppchecksymbols.cpp

@@ -850,7 +850,7 @@ bool CheckSymbols::isTemplateClass(Symbol *symbol) const
     if (symbol) {
         if (Template *templ = symbol->asTemplate()) {
             if (Symbol *declaration = templ->declaration()) {
-                if (declaration->isClass())
+                if (declaration->isClass() || declaration->isForwardClassDeclaration())
                     return true;
             }
         }