Raise ImportError if pyexpat's version is incompatible

Modules/_elementtree.c

@@ -3114,11 +3114,14 @@ PyInit__elementtree(void)
             expat_capi->size < sizeof(struct PyExpat_CAPI) ||
             expat_capi->MAJOR_VERSION != XML_MAJOR_VERSION ||
             expat_capi->MINOR_VERSION != XML_MINOR_VERSION ||
-            expat_capi->MICRO_VERSION != XML_MICRO_VERSION)
-            expat_capi = NULL;
+            expat_capi->MICRO_VERSION != XML_MICRO_VERSION) {
+            PyErr_SetString(PyExc_ImportError,
+                            "pyexpat version is incompatible");
+            return NULL;
         }
-    if (!expat_capi)
+    } else {
         return NULL;
+    }
 #endif
 
     elementtree_parseerror_obj = PyErr_NewException(