problem

Sometimes the merge of terminology tags and track changes tags produced invalid segment content.

Reasons:

1. The split of the string was not unicode save
2. If there were "0" characters in the text, they could be ignored silently in some circumstances (empty vs. is_null problem)

Both problems are solved right now.

The "WARN in editor.terminology.segmentediting: E1132 - Conflict in merging terminology and track changes" warnings are triggered if such invalid segments were produced.