Fix regression from first attempt fixing #5811 (9dce9bddcb)

lib/checknullpointer.cpp

@@ -886,6 +886,8 @@ void CheckNullPointer::nullConstantDereference()
                     if (Token::Match(tok2->previous(), ";|{|}|:|("))
                         break;
                 }
+                if (tok2->previous()->str()=="(")
+                    continue;
                 if (Token::simpleMatch(tok2, "std :: cin"))
                     nullPointerError(tok);
                 if (tok2 && tok2->varId() != 0) {

test/testnullpointer.cpp

@@ -2141,6 +2141,15 @@ private:
               "    return out.str();\n"
               "}n", true, "test.cpp", false);
         ASSERT_EQUALS("", errout.str());
+        // avoid regression from first fix attempt for #5811...
+        check("void deserialize(const std::string &data) {\n"
+              "std::istringstream iss(data);\n"
+              "unsigned int len = 0;\n"
+              "if (!(iss >> len))\n"
+              "    return;\n"
+              "}\n", true, "test.cpp", false);
+        ASSERT_EQUALS("", errout.str());
+
     }
 
     void functioncall() {    // #3443 - function calls