Fixed #3904 (false positive memory leak with linked list)

lib/checkmemoryleak.cpp

@@ -2641,6 +2641,8 @@ void CheckMemoryLeakStructMember::checkStructVariable(const Variable * const var
                 // struct assignment..
                 else if (Token::Match(tok3, "= %varid% ;", structid)) {
                     break;
+                } else if (Token::Match(tok3, "= %var% . %varid% ;", structmemberid)) {
+                    break;
                 }
 
                 // goto isn't handled well.. bail out even though there might be leaks

test/testmemleak.cpp

@@ -4960,6 +4960,9 @@ private:
         // Handle if-else
         TEST_CASE(ifelse);
 
+        // Linked list
+        TEST_CASE(linkedlist);
+
         // struct variable is a global variable
         TEST_CASE(globalvar);
 
@@ -5180,6 +5183,21 @@ private:
         ASSERT_EQUALS("", errout.str());
     }
 
+    void linkedlist() {
+        check("static void foo() {\n"
+              "    struct ABC *abc = malloc(sizeof(struct ABC));\n"
+              "    abc->next = malloc(sizeof(struct ABC));\n"
+              "    abc->next->next = NULL;\n"
+              "\n"
+              "    while (abc) {\n"
+              "        struct ABC *next = abc->next;\n"
+              "        free(abc);\n"
+              "        abc = next;\n"
+              "    }\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void globalvar() {
         check("struct ABC *abc;\n"
               "\n"