Check return value of PyObject_AsFileDescriptor() in _Py_DisplaySourceLine() for error

CID 486768

Python/traceback.c

@@ -255,6 +255,11 @@ _Py_DisplaySourceLine(PyObject *f, PyObject *filename, int lineno, int indent)
 
     /* use the right encoding to decode the file as unicode */
     fd = PyObject_AsFileDescriptor(binary);
+    if (fd < 0) {
+        Py_DECREF(io);
+        Py_DECREF(binary);
+        return NULL;
+    }
     found_encoding = PyTokenizer_FindEncodingFilename(fd, filename);
     encoding = (found_encoding != NULL) ? found_encoding : "utf-8";
     lseek(fd, 0, 0); /* Reset position */