bpo-31546: Fix input hook integration (GH-7978)

Author: tacaswell

Misc/NEWS.d/next/Windows/2018-06-27-23-33-54.bpo-31546.zJlap-.rst

@@ -0,0 +1,3 @@
+Restore running PyOS_InputHook while waiting for user input at the prompt.
+The restores integration of interactive GUI windows (such as Matplotlib
+figures) with the prompt on Windows.

Parser/myreadline.c

@@ -114,6 +114,9 @@ _PyOS_WindowsConsoleReadline(HANDLE hStdIn)
     wbuf = wbuf_local;
     wbuflen = sizeof(wbuf_local) / sizeof(wbuf_local[0]) - 1;
     while (1) {
+        if (PyOS_InputHook != NULL) {
+            (void)(PyOS_InputHook)();
+        }
         if (!ReadConsoleW(hStdIn, &wbuf[total_read], wbuflen - total_read, &n_read, NULL)) {
             err = GetLastError();
             goto exit;