grep: very long lines no longer evoke unwarranted "memory exhausted"

When calling xpalloc (NULL, &n, incr_min, alloc_max, 1) with
nontrivial ALLOC_MAX, this must hold: N + INCR_MIN <= ALLOC_MAX.
With a very long line, it did not, and grep would mistakenly fail
with a report of "memory exhausted".
* src/grep.c (fillbuf): When using nontrivial ALLOC_MAX, ensure it
is at least N+INCR_MIN.
* tests/fillbuf-long-line: New file, to test for this.
* tests/Makefile.am (TESTS): Add its name.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/grep.c b/src/grep.c
index 9c933e46..4109ae46 100644
--- a/src/grep.c
+++ b/src/grep.c
@@ -984,7 +984,7 @@ fillbuf (idx_t save, struct stat const *st)
               ptrdiff_t a;
               if (0 <= to_be_read
                   && INT_ADD_OK (to_be_read, save + min_after_buflim, &a))
-                alloc_max = a;
+                alloc_max = MAX (a, bufalloc + incr_min);
             }
 
           newbuf = xpalloc (NULL, &bufalloc, incr_min, alloc_max, 1);