nvbios/power: Check valid field before printing
nvbios/power: Check valid field before printing

Currently, if an unknown version of a table is encountered, parse functions
will exit without allocating memory for the corresponding NVBIOS sub-structure.
However, print functions only abort if no offset was found (or no table was
found), resulting in a segfault.

karolherbst/envytools,pierremoreau/envytools,MoochMcGee/envytools,kfractal/envytools,grate-driver/envytools,karolherbst/envytools,MoochMcGee/envytools,grate-driver/envytools,envytools/envytools,hakzsam/envytools,karolherbst/envytools,envytools/envytools,pierremoreau/envytools,karolherbst/envytools,kfractal/envytools,grate-driver/envytools,hakzsam/envytools,kfractal/envytools,hakzsam/envytools,MoochMcGee/envytools,MoochMcGee/envytools,hakzsam/envytools,envytools/envytools,pierremoreau/envytools,grate-driver/envytools,pierremoreau/envytools,kfractal/envytools,kfractal/envytools,envytools/envytools,pierremoreau/envytools,MoochMcGee/envytools,hakzsam/envytools,grate-driver/envytools,karolherbst/envytools,envytools/envytools