Segment containing only "0" is not imported

If a segment contains only the string 0, the segment is treated as empty and not imported.

This leads to problems on export and should be fixed. The segment should be imported as a normal segment.

See TS-162 for details.

Use the attached xliff for reproduction.

 => A closer investigation showed, that the issue was also present in the calculation of the segment processing status and in passing segments to the different language resource connectors.