commit 0cb9b40b21e08efc10cd33ead3e4d83c2ff8438b
Author:     linguica <github@andrewstine.org>
AuthorDate: Fri Sep 11 17:05:22 2015 -0700
Commit:     linguica <github@andrewstine.org>
CommitDate: Fri Sep 11 17:05:22 2015 -0700

    Add error message to untagged DR tag crash

    I don't see any real downside in giving the player at least some
    indication of why the game just forcibly quit when they try to use a DR
    special on a 1-sided linedef.
---
 src/doom/p_doors.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/doom/p_doors.c b/src/doom/p_doors.c
index cafab0f4..609aa4e1 100644
--- a/src/doom/p_doors.c
+++ b/src/doom/p_doors.c
@@ -392,6 +392,12 @@ EV_VerticalDoor
     }

     // if the sector has an active thinker, use it
+
+    if (line->sidenum[side^1] == -1)
+    {
+        I_Error("EV_VerticalDoor: DR special type on 1-sided linedef");
+    }
+
     sec = sides[ line->sidenum[side^1]] .sector;

     if (sec->specialdata)