patch 8.1.0840: getchar(0) never returns a character in the terminal

Problem:    getchar(0) never returns a character in the terminal.
Solution:   Call wait_func() at least once.
diff --git a/src/gui_w32.c b/src/gui_w32.c
index c5e5879..ead617a 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -2097,12 +2097,14 @@
 
     s_timed_out = FALSE;
 
-    if (wtime > 0)
+    if (wtime >= 0)
     {
-	/* Don't do anything while processing a (scroll) message. */
+	// Don't do anything while processing a (scroll) message.
 	if (s_busy_processing)
 	    return FAIL;
-	s_wait_timer = (UINT)SetTimer(NULL, 0, (UINT)wtime,
+
+	// When called with "wtime" zero, just want one msec.
+	s_wait_timer = (UINT)SetTimer(NULL, 0, (UINT)(wtime == 0 ? 1 : wtime),
 							 (TIMERPROC)_OnTimer);
     }