Don't try creating an image if the surface is nil

[pointum]

When I deactivate the Client on an iPad (i.e. Home button), the Server crashes on my Mac.

The reason is that SLSDFRDisplayStreamCreate handler block provides nil frameSurface and no error.

TouchBarServer[5528:157215] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', 
reason: 'Invalid parameter not satisfying: ciImage != nil'
*** First throw call stack:
(
0   CoreFoundation          __exceptionPreprocess + 256
1   libobjc.A.dylib         objc_exception_throw + 48
2   CoreFoundation          +[NSException raise:format:arguments:] + 98
3   Foundation              -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 194
4   AppKit                  -[NSBitmapImageRep initWithCIImage:] + 577
5   TouchBarServer          __29-[AppDelegate startStreaming]_block_invoke + 176
6   DFRFoundation           DFRDisplayStream_FrameAvailable + 683
7   DFRFoundation           DFRDisplayStream_server + 286
8   libdispatch.dylib       dispatch_mig_server + 377
9   DFRFoundation           __42-[DFRDisplayStream initWithQueue:handler:]_block_invoke + 92
10  libdispatch.dylib       _dispatch_client_callout + 8
11  libdispatch.dylib       _dispatch_continuation_pop + 563
12  libdispatch.dylib       _dispatch_source_invoke + 2124
13  libdispatch.dylib       _dispatch_workloop_worker_thread + 691
14  libsystem_pthread.dylib _pthread_wqthread + 421
15  libsystem_pthread.dylib start_wqthread + 13
)
...

I’ve added a nil check to fix that.

[AndreasVerhoeven]

Thank you for the work on this :)