C++: Add failing test.

cpp/ql/test/query-tests/Security/CWE/CWE-193/test.cpp

@@ -848,4 +848,15 @@ void test16_with_malloc(size_t index) {
     int* newname = (int*)malloc(size);
     newname[index] = 0; // $ SPURIOUS: alloc=L848 deref=L849 // GOOD [FALSE POSITIVE]
   }
+}
+
+# define MyMalloc(size) malloc(((size) == 0 ? 1 : (size)))
+
+void test_regression(size_t size) {
+  int* p = (int*)MyMalloc(size + 1);
+  int* chend = p + (size + 1);
+
+  if(p <= chend) {
+    *p = 42; // BAD [NOT DETECTED]
+  }
 }