UnicodeDecodeError if unicode characters are entered into the listing search field

[ramonski]

Steps to reproduce

Go to the client listing and search for e.g. süd

Current behavior

UnicodeDecodeError occurs

Expected behavior

Search is working

Screenshot (optional)

Traceback:

2017-11-02T11:04:14 ERROR Bika ClientAnalysisRequestsView: sort_on is 'created', not a valid column
  Module bika.lims.browser.bika_listing, line 1297, in __init__
  Module bechem.lims.browser.clientfolder, line 165, in folderitems
  Module bika.lims.browser.bika_listing, line 1035, in folderitems
  Module Products.AdvancedQuery, line 88, in _evalAdvancedQuery
  Module Products.AdvancedQuery.eval, line 40, in eval
  Module Products.AdvancedQuery.eval, line 16, in _eval
  Module Products.AdvancedQuery.AdvancedQuery, line 220, in _eval
  Module Products.AdvancedQuery.AdvancedQuery, line 233, in _eval
  Module Products.AdvancedQuery.AdvancedQuery, line 84, in _eval
  Module Products.AdvancedQuery.AdvancedQuery, line 279, in _applyIndex
  Module Products.PluginIndexes.common.UnIndex, line 403, in _apply_index
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 1: ordinal not in range(128)
```