fix multi-byte-locale read-beyond-end-of-buffer error

Avoid read-beyond-end-of-buffer errors, evoked by running this:
LC_ALL=en_US.UTF-8 valgrind src/grep -f <(printf 'a\nb\n') <(echo c)

Conditional jump or move depends on uninitialised value(s)
   at 0x78136D: __gconv_transform_utf8_internal (in /lib/libc-2.11.so)
   by 0x7E7232: mbrtowc (in /lib/libc-2.11.so)
   by 0x8055773: dfaexec (dfa.c:2816)
   by 0x804D7B0: EGexecute (search.c:353)
   by 0x804ACD8: grepbuf (grep.c:1036)
   by 0x804B023: grep (grep.c:1156)
   by 0x804B460: grepfile (grep.c:1287)
   by 0x804CF0D: main (grep.c:2282)

Conditional jump or move depends on uninitialised value(s)
   at 0x7E7248: mbrtowc (in /lib/libc-2.11.so)
   by 0x8055773: dfaexec (dfa.c:2816)
   by 0x804D7B0: EGexecute (search.c:353)
   by 0x804ACD8: grepbuf (grep.c:1036)
   by 0x804B023: grep (grep.c:1156)
   by 0x804B460: grepfile (grep.c:1287)
   by 0x804CF0D: main (grep.c:2282)

* src/dfa.c (dfaexec) [MBS_SUPPORT]: Do not access one byte beyond
end of buffer.

0 files changed, 0 insertions, 0 deletions