Fix StructureManager lost logic for null levelAccessor

Author: Doc94

paper-server/patches/sources/net/minecraft/world/level/StructureManager.java.patch

@@ -8,9 +8,9 @@
 +        // Paper start - Fix swamp hut cat generation deadlock
 +        return startsForStructure(sectionX, sectionZ, matcher, this.level);
 +    }
-+    public List<StructureStart> startsForStructure(final int sectionX, final int sectionZ, final Predicate<Structure> matcher, final LevelAccessor level) {
++    public List<StructureStart> startsForStructure(final int sectionX, final int sectionZ, final Predicate<Structure> matcher, final @Nullable LevelAccessor levelAccessor) {
++        Map<Structure, LongSet> allReferences = (levelAccessor == null ? this.level : levelAccessor).getChunk(sectionX, sectionZ, ChunkStatus.STRUCTURE_REFERENCES).getAllReferences();
 +        // Paper end - Fix swamp hut cat generation deadlock
-+        Map<Structure, LongSet> allReferences = level.getChunk(sectionX, sectionZ, ChunkStatus.STRUCTURE_REFERENCES).getAllReferences(); // Paper - Fix swamp hut cat generation deadlock
          Builder<StructureStart> result = ImmutableList.builder();
 
          for (Entry<Structure, LongSet> entry : allReferences.entrySet()) {