MsgDialog: An Abort takes effect from the 8th Update, like on a PSP

Until then the dialog runs normally (and writes result = 0, which an
immediate abort skipped). Measured with one Update per vblank; at one every
other vblank a PSP took 6, so it isn't purely a count.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

test.py

@@ -425,6 +425,7 @@ tests_good = [
   "threads/vtimers/start",
   "threads/vtimers/stop",
   "threads/wakeup/wakeup",
+  "utility/dialog/abort",
   "utility/dialog/htmlviewer",
   "utility/dialog/priority",
   "utility/dialog/status",