Panic if browser binary isn't found

[taladar]

Apparently if the browser binary is not found on the system hxn just panics.

There should be a better error message for this case, especially since the panic just mentions "No such file or directory" but not which path (semantically or the actual value) this refers to.

[pwnwriter]

Right now, i'm able to give some other hints too, but unble to remove panicking :(

[taladar]

You could just exit after printing those hints?

[pwnwriter]

Awh, that was smoooth, thanks

[taladar]

You probably want to set the exit code to something other than 0 since 0 usually indicates a successful operation.