write: fix potential string overflow
Noticed when compiled with gcc verion 9.2.1
20200130.
term-utils/write.c:182:7: warning: ‘strcmp’ argument 1 declared attribute
‘nonstring’ [-Wstringop-overflow=]
182 | if (strcmp(u->ut_line, ctl->src_tty_name) == 0) {
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/utmpx.h:31,
from term-utils/write.c:60:
/usr/include/bits/utmpx.h:59:8: note: argument ‘ut_line’ declared here
59 | char ut_line[__UT_LINESIZE]
| ^~~~~~~
Signed-off-by: Sami Kerola <kerolasa@iki.fi>