lockdown: Plug small memory leak

Credit to Rudolf Tammekivi (Blefish), see issue #599
diff --git a/src/lockdown.c b/src/lockdown.c
index 071697d..9d6d17d 100644
--- a/src/lockdown.c
+++ b/src/lockdown.c
@@ -718,6 +718,7 @@
 			}
 			free(s_version);
 		}
+		plist_free(p_version);
 	}
 
 	userpref_read_pair_record(client_loc->udid, &pair_record);