patch 8.0.0670: can't use input() in a timer callback

Problem:    Can't use input() in a timer callback. (Cosmin Popescu)
Solution:   Reset vgetc_busy and set timer_busy. (Ozaki Kiichi, closes #1790,
            closes #1129)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 7c781d8..581ad7b 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3191,7 +3191,7 @@
 	    ins_typebuf(keys_esc, (remap ? REMAP_YES : REMAP_NONE),
 				  insert ? 0 : typebuf.tb_len, !typed, FALSE);
 	    vim_free(keys_esc);
-	    if (vgetc_busy)
+	    if (vgetc_busy || timer_busy)
 		typebuf_was_filled = TRUE;
 	    if (execute)
 	    {