Issue #15989: Fix several occurrences of integer overflow
when result of PyLong_AsLong() narrowed to int without checks.

This is a backport of changesets 13e2e44db99d and 525407d89277.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index e1df874..80a70b6 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -9640,7 +9640,7 @@
                                     "* wants int");
                     goto onError;
                 }
-                width = PyLong_AsLong(v);
+                width = PyLong_AsSsize_t(v);
                 if (width == -1 && PyErr_Occurred())
                     goto onError;
                 if (width < 0) {
@@ -9677,7 +9677,7 @@
                                         "* wants int");
                         goto onError;
                     }
-                    prec = PyLong_AsLong(v);
+                    prec = _PyLong_AsInt(v);
                     if (prec == -1 && PyErr_Occurred())
                         goto onError;
                     if (prec < 0)