Setting a structure block with NBT provided (no mode set) defaults it to DATA mode

The last of the "change default mode" situations for structure blocks.
It was changed to default to load when placed and set without NBT/state, but the moment you provide any NBT data, it defaults to data once more.

Steps to reproduce:

1. /setblock ~ ~ ~ structure_block

2. Observe it is in LOAD mode.

3. /setblock ~ ~ ~ structure_block{}

4. Observe it is in DATA mode.