Update testleakautovar.cpp

Author: chrchr-github

test/testleakautovar.cpp

@@ -108,6 +108,7 @@ class TestLeakAutoVar : public TestFixture {
         TEST_CASE(doublefree15);
         TEST_CASE(doublefree16);
         TEST_CASE(doublefree17); // #8109: delete with comma operator
+        TEST_CASE(doublefree18);
 
         // exit
         TEST_CASE(exit1);
@@ -1801,6 +1802,18 @@ class TestLeakAutoVar : public TestFixture {
         ASSERT_EQUALS("[test.cpp:5:5] -> [test.cpp:6:16]: (error) Memory pointed to by 'c' is freed twice. [doubleFree]\n", errout_str());
     }
 
+    void doublefree18() {
+        check("typedef struct {\n" // #13918
+              "    FILE * fp;\n"
+              "} S;\n"
+              "void f(S* s, FILE* x) {\n"
+              "    if (fclose(s->fp)) {}\n"
+              "    s->fp = x;\n"
+              "    if (fclose(s->fp)) {}\n"
+              "}\n");
+        ASSERT_EQUALS("", errout_str());
+    }
+
     void exit1() {
         check("void f() {\n"
               "    char *p = malloc(10);\n"