onDidTerminateDebugSession maybe shouldn't fire when debug session doesn't start successfully

[roblourens]

Testing #29490

If a call to createDebugSession fails, e.g. for passing invalid arguments, onDidTerminateDebugSession is still fired. It seems like maybe it shouldn't fire in that case. I don't know whether there are other events in the extension API that follow a similar pattern that we can follow.

[isidorn]

This makes sense to me. @weinand ?

[weinand]

yep, that makes sense. So I suggest that "onDidTerminateDebugSession" is only fired if the corresponding "debugService.createProcess" returns a process. See https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts#L38