Adding Control Reference to Worksheet causes print fail

[xispa]

Description of the issue/feature this PR addresses

Linked issue: #1431

Current behavior before PR

When a reference sample (e.g. control) is added to a Worksheet and the print button is pressed, the following error occurs:

Unable to load the template 'ar_by_column.pt':
Traceback (most recent call last):
  File "/usr/local/Plone/buildout-cache/eggs/senaite.core-1.3.1-py2.7.egg/bika/lims/browser/worksheet/views/printview.py", line 143, in renderWSTemplate
    reptemplate = embed(self)
  File "/usr/local/Plone/buildout-cache/eggs/Zope2-2.13.27-py2.7.egg/Products/Five/browser/pagetemplatefile.py", line 59, in __call__
    sourceAnnotations=getattr(debug_flags, 'sourceAnnotations', 0),
  File "/usr/local/Plone/buildout-cache/eggs/zope.pagetemplate-3.6.3-py2.7.egg/zope/pagetemplate/pagetemplate.py", line 132, in pt_render
    strictinsert=0, sourceAnnotations=sourceAnnotations
  File "/usr/local/Plone/buildout-cache/eggs/five.pt-2.2.4-py2.7.egg/five/pt/engine.py", line 98, in __call__
    return self.template.render(**kwargs)
  File "/usr/local/Plone/buildout-cache/eggs/z3c.pt-3.2.0-py2.7.egg/z3c/pt/pagetemplate.py", line 173, in render
    return base_renderer(**context)
  File "/usr/local/Plone/buildout-cache/eggs/Chameleon-3.6.2-py2.7.egg/chameleon/zpt/template.py", line 306, in render
    return super(PageTemplate, self).render(**_kw)
  File "/usr/local/Plone/buildout-cache/eggs/Chameleon-3.6.2-py2.7.egg/chameleon/template.py", line 209, in render
    raise_with_traceback(exc, tb)
  File "/usr/local/Plone/buildout-cache/eggs/Chameleon-3.6.2-py2.7.egg/chameleon/template.py", line 187, in render
    self._render(stream, econtext, rcontext)
  File "58de6ce66ce9364d2672247d11f82b6c.py", line 119, in render
  File "/usr/local/Plone/buildout-cache/eggs/senaite.core-1.3.1-py2.7.egg/bika/lims/browser/worksheet/views/printview.py", line 190, in getWorksheet
    ws = self._ws_data(self._worksheets[self._current_ws_index])
  File "/usr/local/Plone/buildout-cache/eggs/senaite.core-1.3.1-py2.7.egg/bika/lims/browser/worksheet/views/printview.py", line 253, in _ws_data
    data['ars'] = self._analyses_data(ws)
  File "/usr/local/Plone/buildout-cache/eggs/senaite.core-1.3.1-py2.7.egg/bika/lims/browser/worksheet/views/printview.py", line 375, in _analyses_data
    ar['sample'] = self._sample_data(an.getRequest())
AttributeError: getRequest

 - Expression: "python:view.getWorksheet()"
 - Filename:   ... owser/worksheet/views/../templates/print/ar_by_column.pt
 - Location:   (line 16: col 30)
 - Source:     ... ne="worksheet       python:view.getWorksheet();
                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^
 - Arguments:  repeat: {...} (0)
               template: 
               views: 
               modules: 
               args: 
               here: 
               wrapped_repeat: 
               user: 
               nothing: 
               container: 
               request: 
               traverse_subpath: 
               default: 
               context: 
               view: 
               translate: 
               root: 
               options: {...} (0)
               loop: {...} (0)
               target_language: 

Desired behavior after PR is merged

No traceback and the worksheet print view is rendered correctly

--
I confirm I have tested this PR thoroughly and coded it according to PEP8
and Plone's Python styleguide standards.