Fix: properly map item data back to item mapping.

[oryxel1]

It seems like the client seems to be sending runtimeId=0 for items without a block definition, this causing repeatealy spam of Missing mapping for bedrock item in debug-mode: true and also places where this getMapping was used is broken eg:

Geyser/core/src/main/java/org/geysermc/geyser/translator/protocol/bedrock/BedrockInventoryTransactionTranslator.java

Line 290 in f67cd24

if (packet.getItemInHand() != null && session.getItemMappings().getMapping(packet.getItemInHand()).getJavaItem() instanceof SpawnEggItem) {

, in this case causing multiple entities to spawn when you interact with a water block and also other problems where this method is used, which this pr fix.