Cast to uschar when storing a char in an int that will be used as an index (#88)

* Cast to uschar when storing a char in an int that will be used as an index.
Fixes a heap underflow when the input char has the high bit set and
FS is a regex.

* Add regress test for underflow when RS is a regex and input is 8-bit.

1 files changed, 1 insertions, 1 deletions

diff --git a/b.c b/b.c
index c167b50..a338d43 100644
--- a/b.c
+++ b/b.c
@@ -684,7 +684,7 @@ bool fnematch(fa *pfa, FILE *f, char **pbuf, int *pbufsize, int quantum)
 						FATAL("stream '%.30s...' too long", buf);
 				buf[k++] = (c = getc(f)) != EOF ? c : 0;
 			}
-			c = buf[j];
+			c = (uschar)buf[j];
 			/* assert(c < NCHARS); */
 
 			if ((ns = pfa->gototab[s][c]) != 0)