Crash: when updating a tsv-date series (line diagram) when tsv file reader throws read errors/file missing/invalid data etc.

[ghorwin]

Happens when empty tsv file is updated in session where previously filled tsv file is already used in mapper.

Symptoms:

• filereader plugin does not accept empty tsv file (missing header -> tsv file reader rejects file)
• DataIO reader throws an exception while reading the data -> dataIO remains empty

[ghorwin]

Fixed in rev. 1216