`gsdtool` shouldn't panic when encountering PrmText that violates value constraint

[Rahix]

It seems rather common that PrmText values actually do not fit into the limits imposed by a ExtUserPrmData definition.

Right now, gsdtool simply panics in this situation with a message like:

thread 'main' panicked at gsd-parser/src/lib.rs:214:17:
value 3 not in range 7..=7

Instead we should probably simply issue a warning and opt to continue anyway...

Alternatively, we might want to filter the PrmText for values that are actually allowed. Not sure how others are handling this?