Empty arguments in launch commands are now properly escaped

[meduzik]

Bug discovered with Python debugger extension. Usually, it passes debugOptions array to its python counterpart visualstudio_py_launcher.py from launch.json, joined with comma, like so:

launch.json:
"debugOptions": ["WaitOnAbnormalExit","WaitOnNormalExit"]

launch command:

python C:\Users....vscode\extensions\donjayamanne.python-0.6.3\pythonFiles\PythonTools\visualstudio_py_launcher.py working_dir 51686 34806ad9-833a-45248cd6-18ca4aa74f14 WaitOnAbnormalExit,WaitOnNormalExit file.py

However, when debugOptions is empty, no argument is passed. As visualstudio_py_launcher.py relies on position of its arguments, it breaks, as file.py is now taking place of debugOptions.

I tracked this issue to TerminalSupport.prepareCommand not properly escaping empty argument: it should pass "" instead of empty string for it.

With this fix, launch command for empty debugOptions looks like:

python C:\Users....vscode\extensions\donjayamanne.python-0.6.3\pythonFiles\PythonTools\visualstudio_py_launcher.py working_dir 51686 34806ad9-833a-45248cd6-18ca4aa74f14 "" file.py

and successfully works.

Tested only with cmd.exe, but in my understanding should be the same for other shells, so I changed that too.

[mention-bot]

@dstep, thanks for your PR! By analyzing the history of the files in this pull request, we identified @weinand and @Tyriar to be potential reviewers.

[weinand]

Thanks for the PR.
Since the underlying VS Code source had changed considerably in the meantime, I had to apply the changes from your PR manually. But there will be a "Thank You" in the June release notes.