commit 50ababbd552abfa8ef3b16ccdaea54b58f5c031c
from: Russ Cox <rsc@swtch.com>
date: Tue Jun 03 04:16:48 2014 UTC

acme: fix bufread crash due to typing-point scrolling

Acme tracks the most recent typing insertion point and
the home and end keys stop there on their way
up to the top or down to the bottom of the file.
That point should be iq1, and it should be adjusted
properly so that it's always between 0 and t->file->b.nc inclusive.
(This is all code from an external contributor, years old at this
point but new since Plan 9.)

Somehow, sometimes iq1 ends up a little beyond b.nc,
and when passed to textbacknl it crashes acme in bufread.
I can't see how that can happen but if it does, avoid the crash.

It's tempting to pull the insertion point code out entirely
but this is a little less invasive and should fix things for now.

TBR=rsc
https://codereview.appspot.com/107730043

commit - 6400c9f20c3cdab491cd2aec29cfd2ae632d5046
commit + 50ababbd552abfa8ef3b16ccdaea54b58f5c031c
blob - 463db9ff623b8fc8c10f7b10e341e8aa3bb8acca
blob + c537d277f55dc3327e608443b19cb6c12b9341c6
--- src/cmd/acme/text.c
+++ src/cmd/acme/text.c
@@ -725,6 +725,10 @@ texttype(Text *t, Rune r)
 	case Kend:
 		typecommit(t);
 		if(t->iq1 > t->org+t->fr.nchars) {
+			if(t->iq1 > t->file->b.nc) {
+				// should not happen, but does. and it will crash textbacknl.
+				t->iq1 = t->file->b.nc;
+			}
 			q0 = textbacknl(t, t->iq1, 1);
 			textsetorigin(t, q0, TRUE);
 		} else