1.13 doesn't convert old structures correctly

Step 1: Make a structure in 1.12.2 that has non-decayable leaves in it. (4 <= data value <= 7)

Step 2: Move structure into a data pack in a 1.13.2 world.

Step 3: Load the structure in 1.13.2, notice that the leaves start decaying.

Apparently, MC doesn't convert the 'decayable' data value to the inverse 'persistent' block state.

Tested saving in 1.12.2 and loading in 1.13.2 and 18w50a