fix: Handle gamescope not being present

[rfrench3]

When gamescope is not present on the system and SCB_NOSCOPE does not equal 1, scopebuddy does not launch anything.

Current behavior without gamescope present (tested in a virtual machine and distrobox, program does not launch):

Running ScopeBuddy version: 1.2.5
Launching: env -u LD_PRELOAD gamescope  -- env LD_PRELOAD=  "glxgears"
bash: gamescope: command not found

New behavior (program does launch):

Running ScopeBuddy version: 1.2.5
Setting SCB_NOSCOPE=1 because gamescope was not found