bpo-40263: Fixes an off-by-one error in _winapi_WaitForMultipleObjects_impl (GH-19501)

(cherry picked from commit 92b5dc7)

Co-authored-by: Ray Donnelly <[email protected]>

Author: miss-islington

Misc/NEWS.d/next/Windows/2020-04-13-15-20-28.bpo-40263.1KKEbu.rst

@@ -0,0 +1,3 @@
+This is a follow-on bug from https://bugs.python.org/issue26903. Once that
+is applied we run into an off-by-one assertion problem. The assert was not
+correct.

Modules/_winapi.c

@@ -1713,7 +1713,7 @@ _winapi_WaitForMultipleObjects_impl(PyObject *module, PyObject *handle_seq,
     nhandles = PySequence_Length(handle_seq);
     if (nhandles == -1)
         return NULL;
-    if (nhandles < 0 || nhandles >= MAXIMUM_WAIT_OBJECTS - 1) {
+    if (nhandles < 0 || nhandles > MAXIMUM_WAIT_OBJECTS - 1) {
         PyErr_Format(PyExc_ValueError,
                      "need at most %zd handles, got a sequence of length %zd",
                      MAXIMUM_WAIT_OBJECTS - 1, nhandles);