[lldb] Check that qLaunchGDBServer packet does not return an error

While looking at https://github.com/llvm/llvm-project/issues/61955
I noticed that when we send qLaunchGDBServer we check that we got a response
but not what kind of response it was.

I think this was why the bug reporter saw:
(lldb) run
error: invalid host:port specification: '[192.168.64.2]'

The missing port is because we went down a path we only should have
chosen if the operation succeeded. Since we didn't check, we went ahead
with an empty port number.

To test this I've done the following:
* Make a temporary copy of lldb-server.
* Run that as a platform.
* Remove the copy.
* Attempt to create and run a target.

This fails because the running lldb-server will try to invoke itself
and it no longer exists.

Reviewed By: jasonmolenda

Differential Revision: https://reviews.llvm.org/D153513