sway: commands: exec: restore SIGPIPE before exec:ing

Sway ignores SIGPIPE (by installing a SIG_IGN handler), in order to
“prevent IPC from crashing Sway”.

SIG_IGN handlers are the *only* signal handlers inherited in
sub-processes. As such, we should be a good citizen and restore
the SIGPIPE handler to its default handler.

Original bug report:
https://www.mail-archive.com/debian-bugs-dist@lists.debian.org/msg1806907.html

sway/commands/exec_always.c

@@ -57,6 +57,7 @@ struct cmd_results *cmd_exec_process(int argc, char **argv) {
 		sigset_t set;
 		sigemptyset(&set);
 		sigprocmask(SIG_SETMASK, &set, NULL);
+		signal(SIGPIPE, SIG_DFL);
 		close(fd[0]);
 		if ((child = fork()) == 0) {
 			close(fd[1]);