Make several deathmatch tweaks

- Remove its fountains. We had previously removed water in this arena
  because it allowed the player to score an easy kill by freezing and
  melting the water under the NPC. Word has spread that you can do the
  same thing by digging the fountains first to make your own pools.
  (Also, there's no particular reason to give the player extra
  opportunities for water demon wishes or Excalibur, thus making the
  game easier. These were here only for effect.)
- Add a livelog for fleeing the deathmatch.
- Fix segfault when loading the deathmatch with no NPC files available -
  this is because pick_npc_file was changed to return a null when its
  calling code assumed it would always be returned a valid pointer.
  Restore that assumption.

dat/npcdeath.des

@@ -47,8 +47,6 @@ NON_DIGGABLE:(0,0,75,19)
 ENGRAVING:(54,09),burn,"Point of no return"
 ENGRAVING:(60,09),burn,"Two players enter, one player leaves..."
 
-FOUNTAIN:(64,08)
-FOUNTAIN:(64,10)
 DOOR:closed,(53,09)
 
 # Statues of those before...

src/files.c

@@ -5076,15 +5076,15 @@ pick_npc_file(VOID_ARGS)
     DIR *d = opendir(TNNT_NPC_DIR);
     int chance = 0;
     struct dirent *de;
+    npcpath[0] = '\0';
     if (!d) {
         const char *errormsg;
         if (!(errormsg = strerror(errno)))
             errormsg = "unknown error";
         impossible("can't open NPC directory at %s (%s)",
                    TNNT_NPC_DIR, errormsg);
-        return (char *) 0;
+        return npcpath; /* with leading \0 */
     }
-    npcpath[0] = '\0';
     while ((de = readdir(d)) != NULL) {
         if (!strncmp(de->d_name, "NPC-", 4)
             && !rn2(++chance)) {

src/teleport.c

@@ -1084,6 +1084,7 @@ register struct trap *ttmp;
             deltrap(ttmp);    /* destroy this portal - maybe unnecessary */
             portal_flag = -1; /* destroy corresponding portal */
             msg = "Loud booing follows you out of the arena...";
+            livelog_printf(LL_UMONST, "cowardly fled from the Arena");
         }
     }