Preserve <256 block IDs for terrain generation

If a block ID is below 256, we'll keep it below 256. This is
required by certain blocks - or actually, only terrain generation
blocks. If an >256 ID is used it'll be truncated with disastrous
results, like turning all your topsoil to saplings causing
stack overflows on block updates: https://github.com/MinecraftPortCentral/MCPC-Plus/issues/707

ShaRose's ID Resolver has an @IDRestrictionAnnotation mods can use
to tell it not to resolve >256, example: https://github.com/ExtrabiomesXL/ExtrabiomesXL/blob/master/common/extrabiomes/utility/IDRestrictionAnnotation.java
However not all mods use it. Some will bail on >256 IDs, but others
will silently let you use the ID. Hit this with Mo' Creatures wyvern.

So leave the <256 IDs <256 ID, should fix these issues at the cost of
possibly using lower block IDs than necessary. If the defaults are >256
they'll be resolved as 4096-block IDs as usual.