Dont use ctypes for setmaxstdio() on windows

Once we move to the Universal CRT ctypes will not be able to load libc
at all.

src/calibre/startup.py

@@ -64,11 +64,8 @@ if not _run_once:
     # Ensure that the max number of open files is at least 1024
     if iswindows:
         # See https://msdn.microsoft.com/en-us/library/6e3b887c.aspx
-        import ctypes
+        if hasattr(winutil, 'setmaxstdio'):
-        msvcrt = ctypes.cdll.msvcrt
+            winutil.setmaxstdio(max(1024, winutil.getmaxstdio()))
-        soft, hard = msvcrt._getmaxstdio(), 2048
-        if soft < 1024:
-            msvcrt._setmaxstdio(min(1024, hard))
     else:
         import resource
         soft, hard = resource.getrlimit(resource.RLIMIT_NOFILE)

src/calibre/utils/windows/winutil.c

@@ -215,6 +215,19 @@ winutil_prepare_for_restart(PyObject *self, PyObject *args) {
     Py_RETURN_NONE;
 }
 
+static PyObject *
+winutil_get_max_stdio(PyObject *self, PyObject *args) {
+	return Py_BuildValue("i", _getmaxstdio());
+}
+ 
+static PyObject *
+winutil_set_max_stdio(PyObject *self, PyObject *args) {
+	int num = 0;
+	if (!PyArg_ParseTuple(args, "i", &num)) return NULL;
+	if (_setmaxstdio(num) == -1) return PyErr_SetFromErrno(PyExc_ValueError);
+	Py_RETURN_NONE;
+}
+ 
 static PyObject *
 winutil_strftime(PyObject *self, PyObject *args)
 {
@@ -360,6 +373,14 @@ be a unicode string. Returns unicode strings."
         "prepare_for_restart()\n\nRedirect output streams so that the child process does not lock the temp files"
     },
 
+    {"getmaxstdio", winutil_get_max_stdio, METH_VARARGS,
+        "getmaxstdio()\n\nThe maximum number of open file handles."
+    },
+
+    {"setmaxstdio", winutil_set_max_stdio, METH_VARARGS,
+        "setmaxstdio(num)\n\nSet the maximum number of open file handles."
+    },
+
     {NULL, NULL, 0, NULL}
 };