CppTools: Deduplicate null validation

Change-Id: I291fd7d755f08a533bb2686024858b11fabd9bed
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/cpptools/cppcompletionassist.cpp

@@ -1888,8 +1888,7 @@ bool CppCompletionAssistProcessor::completeConstructorOrFunction(const QList<CPl
             if (doc->parse(Document::ParseDeclaration)) {
                 doc->check();
                 if (SimpleDeclarationAST *sd = doc->translationUnit()->ast()->asSimpleDeclaration()) {
-                    if (sd->declarator_list &&
-                        sd->declarator_list && sd->declarator_list->value->postfix_declarator_list
+                    if (sd->declarator_list && sd->declarator_list->value->postfix_declarator_list
                         && sd->declarator_list->value->postfix_declarator_list->value->asFunctionDeclarator()) {
 
                         autocompleteSignature = true;