Separate handling of Unicode and other errors

In the initial implementation, errors other than encoding errors would
both raise an error indicating an invalid format, which would not be
true for errors like MemoryError.

Author: pganssle

Modules/_datetimemodule.c

@@ -4911,7 +4911,12 @@ datetime_fromisoformat(PyObject* cls, PyObject *dtstr) {
     const char * dt_ptr = PyUnicode_AsUTF8AndSize(dtstr_clean, &len);
 
     if (dt_ptr == NULL) {
-        goto invalid_string_error;
+        if (PyErr_ExceptionMatches(PyExc_UnicodeEncodeError)) {
+            // Encoding errors are invalid string errors at this point
+            goto invalid_string_error;
+        } else {
+            goto error;
+        }
     }
 
     const char *p = dt_ptr;