Issue #10989: Fix a crash on SSLContext.load_verify_locations(None, True).

Patch reviewed by Antoine Pitrou, okayed by Georg Brandl.
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index 1e4b38a..141b1ae 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -1683,7 +1683,7 @@
         return NULL;
     }
     if (capath && !PyUnicode_FSConverter(capath, &capath_bytes)) {
-        Py_DECREF(cafile_bytes);
+        Py_XDECREF(cafile_bytes);
         PyErr_SetString(PyExc_TypeError,
                         "capath should be a valid filesystem path");
         return NULL;