Goto error immediately if we can't get handle to io.open

Author: johnslavik

Objects/call.c

@@ -729,9 +729,6 @@ _Py_COMP_DIAG_POP
 PyObject * _PyObject_CallMethodFormat(PyThreadState *tstate, PyObject *callable,
                                       const char *format, ...)
 {
-    if (callable == NULL) {
-        return NULL;
-    }
     va_list va;
     va_start(va, format);
     PyObject *retval = callmethod(tstate, callable, format, va);

Python/traceback.c

@@ -415,6 +415,9 @@ _Py_FindSourceFile(PyObject *filename, char* namebuf, size_t namelen, PyObject *
     npath = PyList_Size(syspath);
 
     open = PyObject_GetAttr(io, &_Py_ID(open));
+    if (open == NULL) {
+        goto error;
+    }
     for (i = 0; i < npath; i++) {
         v = PyList_GetItem(syspath, i);
         if (v == NULL) {