Do not schedule to main for getChunkImmediately type calls (#2362)

They are MT-Safe already. These changes reduce deadlock chances
given these calls are used in Entity#isValid(), and plugins
check this in packet handling...

Spigot-Server-Patches/Fix-World-isChunkGenerated-calls.patch

@@ -8,7 +8,7 @@ This patch also adds a chunk status cache on region files (note that
 its only purpose is to cache the status on DISK)
 
 diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
-index 220cd197fa..775b5f7fe3 100644
+index 9765eaf24c..d714b8d01b 100644
 --- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
 +++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
 @@ -0,0 +0,0 @@ public class ChunkProviderServer extends IChunkProvider {
@@ -27,24 +27,9 @@ index 220cd197fa..775b5f7fe3 100644
 +
 +    @Nullable
 +    public IChunkAccess getChunkAtImmediately(int x, int z) {
-+        if (Thread.currentThread() != this.serverThread) {
-+            return CompletableFuture.supplyAsync(() -> {
-+                return this.getChunkAtImmediately(x, z);
-+            }, this.serverThreadQueue).join();
-+        }
-+
 +        long k = ChunkCoordIntPair.pair(x, z);
 +
-+        IChunkAccess ichunkaccess;
-+
-+        for (int l = 0; l < 4; ++l) {
-+            if (k == this.cachePos[l]) {
-+                ichunkaccess = this.cacheChunk[l];
-+                if (ichunkaccess != null) { // CraftBukkit - the chunk can become accessible in the meantime TODO for non-null chunks it might also make sense to check that the chunk's state hasn't changed in the meantime
-+                    return ichunkaccess;
-+                }
-+            }
-+        }
++        // Note: Bypass cache to make this MT-Safe
 +
 +        PlayerChunk playerChunk = this.getChunk(k);
 +        if (playerChunk == null) {