Fixed #2168 (Segmentation fault of cppcheck)

lib/checkpostfixoperator.cpp

@@ -37,7 +37,13 @@ void CheckPostfixOperator::postfixOperator()
     if (!_settings->_checkCodingStyle)
         return;
 
-    for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
+    const Token *tok = _tokenizer->tokens();
+
+    // prevent crash if first token is ++ or --
+    if (Token::Match(tok, "++|--"))
+        tok = tok->next();
+
+    for (; tok; tok = tok->next())
     {
         bool result = false;
         if (Token::Match(tok, "++|--"))

test/testpostfixoperator.cpp

@@ -67,6 +67,7 @@ private:
         TEST_CASE(teststream);
         TEST_CASE(testvolatile);
         TEST_CASE(testiterator);
+        TEST_CASE(test2168);
     }
 
     void testsimple()
@@ -364,7 +365,12 @@ private:
 
     }
 
-
+    void test2168()
+    {
+        check("--> declare allocator lock here\n"
+              "int main(){}\n");
+        ASSERT_EQUALS("", errout.str());
+    }
 };
 
 REGISTER_TEST(TestPostfixOperator)