Add missing return when datafixers fail for chunk conversion

Caused the chunk to be later deserialized, which would
result in spamming unrelated errors (possibly) +
double chunk completion.

Author: Spottedleaf

patches/server/0258-Asynchronous-chunk-IO-and-loading.patch

@@ -1442,10 +1442,10 @@ index 0000000000000000000000000000000000000000..ee906b594b306906c170180a29a8b619
 +}
 diff --git a/src/main/java/com/destroystokyo/paper/io/chunk/ChunkLoadTask.java b/src/main/java/com/destroystokyo/paper/io/chunk/ChunkLoadTask.java
 new file mode 100644
-index 0000000000000000000000000000000000000000..c5924b64604a678f7efdc0c2ce8070c9239dcf18
+index 0000000000000000000000000000000000000000..79082639d9238c62c896dfc025ede92c88680954
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/io/chunk/ChunkLoadTask.java
-@@ -0,0 +1,137 @@
+@@ -0,0 +1,138 @@
 +package com.destroystokyo.paper.io.chunk;
 +
 +import co.aikar.timings.Timing;
@@ -1544,6 +1544,7 @@ index 0000000000000000000000000000000000000000..c5924b64604a678f7efdc0c2ce8070c9
 +            } catch (final Throwable ex) {
 +                PaperFileIOThread.LOGGER.error("Could not apply datafixers for chunk task: " + this.toString(), ex);
 +                this.complete(ChunkLoadTask.createEmptyHolder());
++                return;
 +            }
 +
 +            if (this.checkCancelled()) {