Revert "Remove unnecessary condition check"

This reverts commit ceb9b1f6ec.

I need to look at this again, there is a report that commit in question
may cause problems and apparently logic may have failed me when I
removed this code, as it probably should stay and everything after it is
unreacheable.

Signed-off-by: Amadeusz Sławiński <amade@asmblr.net>

src/attacher.c

@@ -235,6 +235,8 @@ int Attach(int how)
 			pause();	/* wait for SIGCONT */
 		xsignal(SIGCONT, SIG_DFL);
 		ContinuePlease = false;
+		if (how != MSG_ATTACH)
+			return 0;	/* we detached it. jw. */
 		sleep(1);	/* we dont want to overrun our poor backend. jw. */
 		if ((lasts = MakeClientSocket(0)) == -1)
 			Panic(0, "Cannot contact screen again. Sigh.");