Issue #15989: Fix several occurrences of integer overflow
when result of PyInt_AsLong() or 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 79e1b60..46bfe2b 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -8411,7 +8411,9 @@
                                     "* wants int");
                     goto onError;
                 }
-                width = PyInt_AsLong(v);
+                width = PyInt_AsSsize_t(v);
+                if (width == -1 && PyErr_Occurred())
+                    goto onError;
                 if (width < 0) {
                     flags |= F_LJUST;
                     width = -width;
@@ -8446,7 +8448,9 @@
                                         "* wants int");
                         goto onError;
                     }
-                    prec = PyInt_AsLong(v);
+                    prec = _PyInt_AsInt(v);
+                    if (prec == -1 && PyErr_Occurred())
+                        goto onError;
                     if (prec < 0)
                         prec = 0;
                     if (--fmtcnt >= 0)