Fixed #2437 (false positive: possible null pointer dereference: tok2)

lib/checknullpointer.cpp

@@ -461,7 +461,7 @@ void CheckNullPointer::nullPointerByDeRefAndChec()
                     break;
                 }
 
-                if (tok1->varId() == varid)
+                if (tok1->varId() == varid && !Token::Match(tok1->previous(), "[?:]"))
                 {
                     // unknown : this is set by isPointerDeRef if it is
                     //           uncertain

test/testnullpointer.cpp

@@ -397,6 +397,14 @@ private:
               "        ;\n"
               "}\n");
         ASSERT_EQUALS("", errout.str());
+
+        check("void foo(struct ABC *abc)\n"
+              "{\n"
+              "    abc = abc ? abc->next : 0;\n"
+              "    if (!abc)\n"
+              "        ;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void nullpointer5()