[ronie]

2017-02-24 drop support for using hyphen as none value

as of today, please do not use a hyphen '-' as an empty value.

tags like these are no longer supported:
<label>-</label>
<image>-</image>

you can simply use:
<label></label>
<image></image>

or if you prefer the alternate format:
<label/>
<image/>


pull-request: https://github.com/xbmc/xbmc/pull/10389
commit: https://github.com/xbmc/xbmc/commit/e1c2...22cd9ce86e