CompoundTag: quietly ignore repeated keys, instead of throwing

this isn't ideal, but we don't have much of a choice; many chunks in very old PM worlds are affected by the furnace bug (basically any chunk with a furnace);
we have no other way to avoid losing the entire chunk to corruption errors

src/tag/CompoundTag.php

@@ -24,7 +24,6 @@
 namespace pocketmine\nbt\tag;
 
 use pocketmine\nbt\NBT;
-use pocketmine\nbt\NbtDataException;
 use pocketmine\nbt\NbtStreamReader;
 use pocketmine\nbt\NbtStreamWriter;
 use pocketmine\nbt\NoSuchTagException;
@@ -292,7 +291,12 @@ public static function read(NbtStreamReader $reader, ReaderTracker $tracker) : s
 				$name = $reader->readString();
 				$tag = NBT::createTag($type, $reader, $tracker);
 				if($result->getTag($name) !== null){
-					throw new NbtDataException("Duplicate key \"$name\"");
+					//this is technically a corruption case, but it's very common on older PM worlds (pretty much every
+					//furnace in PM worlds prior to 2017 is affected), and since we can't extricate this borked data
+					//from the rest in Anvil/McRegion worlds, we can't barf on this - it would result in complete loss
+					//of the chunk.
+					//TODO: add a flag to enable throwing on this (strict mode)
+					continue;
 				}
 				$result->setTag($name, $tag);
 			}