tools: mdbus2: fix bug that we can't supply an empty string as argument
tools: mdbus2: fix bug that we can't supply an empty string as argument

If you want to supply an empty string as argument you have to pass at least
"" or '' so the commandline parser detects that the argument is empty.

Signed-off-by: Simon Busch <e923d8431f09840b119134ca71ec8d74989d15cc@gravedo.de>

slyon/debian-fso-usaged,slyon/debian-fso-usaged,slyon/debian-fso-deviced,slyon/debian-fso-deviced