Sync sector tags and tag list variables properly

Dunno who thought it was a good idea to lump tag, nexttag and firsttag together in $$$.sav, but that meant changing sector tags caused SRB2 to stop responding since it lead to the tag lists being broken

src/p_saveg.c

@@ -460,6 +460,7 @@ static void P_NetUnArchivePlayers(void)
 #define SD_TAG       0x10
 #define SD_FLOORANG  0x20
 #define SD_CEILANG   0x40
+#define SD_TAGLIST   0x80
 
 #define LD_FLAG     0x01
 #define LD_SPECIAL  0x02
@@ -535,6 +536,8 @@ static void P_NetArchiveWorld(void)
 
 		if (ss->tag != SHORT(ms->tag))
 			diff2 |= SD_TAG;
+		if (ss->nexttag != ss->spawn_nexttag || ss->firsttag != ss->spawn_firsttag)
+			diff2 |= SD_TAGLIST;
 
 		// Check if any of the sector's FOFs differ from how they spawned
 		if (ss->ffloors)
@@ -582,16 +585,17 @@ static void P_NetArchiveWorld(void)
 				WRITEFIXED(put, ss->ceiling_xoffs);
 			if (diff2 & SD_CYOFFS)
 				WRITEFIXED(put, ss->ceiling_yoffs);
-			if (diff2 & SD_TAG)
+			if (diff2 & SD_TAG) // save only the tag
-			{
 				WRITEINT16(put, ss->tag);
-				WRITEINT32(put, ss->firsttag);
-				WRITEINT32(put, ss->nexttag);
-			}
 			if (diff2 & SD_FLOORANG)
 				WRITEANGLE(put, ss->floorpic_angle);
 			if (diff2 & SD_CEILANG)
 				WRITEANGLE(put, ss->ceilingpic_angle);
+			if (diff2 & SD_TAGLIST) // save both firsttag and nexttag
+			{ // either of these could be changed even if tag isn't
+				WRITEINT32(put, ss->firsttag);
+				WRITEINT32(put, ss->nexttag);
+			}
 
 			// Special case: save the stats of all modified ffloors along with their ffloor "number"s
 			// we don't bother with ffloors that haven't changed, that would just add to savegame even more than is really needed
@@ -774,12 +778,11 @@ static void P_NetUnArchiveWorld(void)
 		if (diff2 & SD_CYOFFS)
 			sectors[i].ceiling_yoffs = READFIXED(get);
 		if (diff2 & SD_TAG)
+			sectors[i].tag = READINT16(get); // DON'T use P_ChangeSectorTag
+		if (diff2 & SD_TAGLIST)
 		{
-			INT16 tag;
-			tag = READINT16(get);
 			sectors[i].firsttag = READINT32(get);
 			sectors[i].nexttag = READINT32(get);
-			P_ChangeSectorTag(i, tag);
 		}
 		if (diff2 & SD_FLOORANG)
 			sectors[i].floorpic_angle  = READANGLE(get);

src/p_setup.c

@@ -614,6 +614,7 @@ static void P_LoadSectors(lumpnum_t lumpnum)
 		ss->special = SHORT(ms->special);
 		ss->tag = SHORT(ms->tag);
 		ss->nexttag = ss->firsttag = -1;
+		ss->spawn_nexttag = ss->spawn_firsttag = -1;
 
 		memset(&ss->soundorg, 0, sizeof(ss->soundorg));
 		ss->validcount = 0;

src/p_spec.c

@@ -1519,6 +1519,8 @@ static inline void P_InitTagLists(void)
 		size_t j = (unsigned)sectors[i].tag % numsectors;
 		sectors[i].nexttag = sectors[j].firsttag;
 		sectors[j].firsttag = (INT32)i;
+		sectors[i].spawn_nexttag = sectors[i].nexttag;
+		sectors[j].spawn_firsttag = sectors[j].firsttag;
 	}
 
 	for (i = numlines - 1; i != (size_t)-1; i--)

src/r_defs.h

@@ -383,6 +383,7 @@ typedef struct sector_s
 #endif
 
 	// these are saved for netgames, so do not let Lua touch these!
+	INT32 spawn_nexttag, spawn_firsttag; // the actual nexttag/firsttag values may differ if the sector's tag was changed
 
 	// offsets sector spawned with (via linedef type 7)
 	fixed_t spawn_flr_xoffs, spawn_flr_yoffs;