bpo-36301: Error if decoding pybuilddir.txt fails (GH-12422)

Python initialization now fails if decoding pybuilddir.txt
configuration file fails at startup.

_PyPathConfig_Calculate() now reports memory allocation failure and
decoding error on decoding pybuilddir.txt content from
UTF-8/surrogateescape.

Python/pathconfig.c

@@ -712,7 +712,7 @@ _Py_FindEnvConfigValue(FILE *env_file, const wchar_t *key,
             continue;
         }
 
-        wchar_t *tmpbuffer = _Py_DecodeUTF8_surrogateescape(buffer, n);
+        wchar_t *tmpbuffer = _Py_DecodeUTF8_surrogateescape(buffer, n, NULL);
         if (tmpbuffer) {
             wchar_t * state;
             wchar_t * tok = WCSTOK(tmpbuffer, L" \t\r\n", &state);