envydis: Fix segfault when ISA has no variants.
envydis: Fix segfault when ISA has no variants.

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