Work around error message in formatter selection

[schulmar]

When the Clang Format Plugin formatter is selected, the example code is formatted by it.
However, it is not a file so there is no path that can be passed to clang-format.

When an editor is active in the background, the file's path of this editor will be used but this might be misleading.

The best would probably be to use the workspace or project path (depending on the settings dialog) for the formatter test code.