(#1067) Fix attach process by name error: index out of range

[michalbiesek]

• provide exit status message without panic

Closes #1067

Test instructions:

docker run --privileged --rm -it cribl/scope:dev-x86_64
top &
top &
scope attach top
Found multiple processes matching that name...
ID	PID	USER	SCOPED	COMMAND
1 	16 	root	false 	top
2 	17 	root	false 	top
Select an ID from the list:

When choosing 3, you should see:

Invalid Selection

Instead of panic described in #1067

[jrcheli]

Looks great! Merging!