Fix incorrect handling of mustNotSave

CB used the dirty flag to construct the chunk unload event,
but then sets mustNotSave to the inverted value of the event
after calling the event without considering that the chunk may
actually be brought up to loaded status again later. Then, CB
overrides the isUnsaved method of LevelChunk to additionally
use mustNotSave.

Thus, if the chunk is not marked dirty when unloading, the
mustNotSave value will be set to true. Then, once the chunk
is reloaded and edited the dirty flag will be set. However,
when unloading the chunk finally, the isUnsaved method
will return false due to mustNotSave being true. Thus, the
chunk will never be saved.

To fix these issues, no longer make mustNotSave override
isUnsaved and always set the save flag for the chunk unload
event.

This issue started popping up recently due to the recent
change to mark chunks as not dirty after saving them, which
increased the chance of the save issue occurring in the first
place.

patches/server/0016-Rewrite-chunk-system.patch

@@ -16675,7 +16675,7 @@ index e6240f891e396d91e31b02fdf3084be77e9d6697..00cb9dafc711607f28529ea9afbcdb49
  
      public int getIndex() {
 diff --git a/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java b/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
-index e75ec8f6aa597b5f3048d6269fba45eef057bc71..0e2a15d623e5ff5c34252e4b714713a6a670e755 100644
+index e75ec8f6aa597b5f3048d6269fba45eef057bc71..81092acad680e6c797745d24badba4dd488bb246 100644
 --- a/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
 +++ b/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
 @@ -183,6 +183,43 @@ public class LevelChunk extends ChunkAccess {
@@ -16819,16 +16819,27 @@ index e75ec8f6aa597b5f3048d6269fba45eef057bc71..0e2a15d623e5ff5c34252e4b714713a6
  
              if (this.needsDecoration) {
                  try (co.aikar.timings.Timing ignored = this.level.timings.chunkLoadPopulate.startTiming()) { // Paper
-@@ -716,7 +817,9 @@ public class LevelChunk extends ChunkAccess {
+@@ -716,8 +817,10 @@ public class LevelChunk extends ChunkAccess {
      }
  
      public void unloadCallback() {
 +        if (!this.loadedTicketLevel) { LOGGER.error("Double calling chunk unload!", new Throwable()); } // Paper
          org.bukkit.Server server = this.level.getCraftServer();
+-        org.bukkit.event.world.ChunkUnloadEvent unloadEvent = new org.bukkit.event.world.ChunkUnloadEvent(this.bukkitChunk, this.isUnsaved());
 +        this.chunkHolder.getEntityChunk().callEntitiesUnloadEvent(); // Paper - rewrite chunk system
-         org.bukkit.event.world.ChunkUnloadEvent unloadEvent = new org.bukkit.event.world.ChunkUnloadEvent(this.bukkitChunk, this.isUnsaved());
++        org.bukkit.event.world.ChunkUnloadEvent unloadEvent = new org.bukkit.event.world.ChunkUnloadEvent(this.bukkitChunk, true); // Paper - rewrite chunk system - force save to true so that mustNotSave is correctly set below
          server.getPluginManager().callEvent(unloadEvent);
          // note: saving can be prevented, but not forced if no saving is actually required
+         this.mustNotSave = !unloadEvent.isSaveChunk();
+@@ -741,7 +844,7 @@ public class LevelChunk extends ChunkAccess {
+ 
+     @Override
+     public boolean isUnsaved() {
+-        return super.isUnsaved() && !this.mustNotSave;
++        return super.isUnsaved(); // Paper - rewrite chunk system - do NOT clobber the dirty flag
+     }
+     // CraftBukkit end
+ 
 @@ -804,7 +907,10 @@ public class LevelChunk extends ChunkAccess {
          });
      }