Ignore daemon lock file if the daemon process died.

Do this in a fashion similar to what was done in commit
6ff95238766656c5ea9d5c65c35d3aef93499f60.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/dmon.c

@@ -214,6 +214,6 @@ dmon_stop (void)
   if (!dpid)
     return;
 
-  if (kill ((pid_t)dpid, SIGINT) < 0)
+  if (kill ((pid_t)dpid, SIGINT) < 0 && errno != ESRCH)
     EXIT (_("Could not stop calcurse daemon: %s\n"), strerror (errno));
 }