[Refacor/Bugfix] Clear only fluid nbt for GTFluidHandlerItemStack

[MCTian-mi]

What

The implementation of GTFluidHandlerItemStack clears the entire tag compound when fluids are drained:

GregTech/src/main/java/gregtech/api/capability/impl/GTFluidHandlerItemStack.java

Lines 85 to 89 in 70bfc8a

	private void removeTagWhenEmpty(boolean doDrain) {
	if (doDrain && this.getFluid() == null) {
	this.container.setTagCompound(null);
	}
	}

This causes other NBT datas to be purged together, e.g. the lockedFluid for quantum tanks. (btw the locked fluid don't work for item stacks)

Implementation Details

The removeTagWhenEmpty method is removed completely, since Forge handles fluid nbt clearing itself alr in FluidHandlerItemStack#setContainerToEmpty:

/**
 * Override this method for special handling.
 * Can be used to swap out or destroy the container.
 */
protected void setContainerToEmpty() {
    container.getTagCompound().removeTag(FLUID_NBT_KEY);
}

This clears only the NBT tag about the fluid contained within. An extra check was added to remove the NBT when empty:

@Override
protected void setContainerToEmpty() {
    super.setContainerToEmpty();
    var tag = container.getTagCompound();
    if (tag != null && tag.isEmpty()) {
        container.setTagCompound(null);
    }
}