[FIX] owpaintdata: Fix an error when the input dataset contains NaN

[ales-erjavec]

Issue

Input

X1,X2,D
c,c,d
,,class
1,1,a
1,1,?
2,1,b

To Paint Data widget (i.e. an unknown in the class column)

-> On current master

Traceback (most recent call last):
  File "/Users/aleserjavec/workspace/orange3/Orange/canvas/scheme/widgetsscheme.py", line 822, in process_signals_for_widget
    handler(*args)
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/data/owpaintdata.py", line 1029, in set_data
    self.reset_to_input()
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/data/owpaintdata.py", line 1051, in reset_to_input
    self._replot()
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/data/owpaintdata.py", line 1237, in _replot
    pen = [pens[ci] for ci in self.__buffer[:, 2].astype(int)]
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/data/owpaintdata.py", line 1237, in <listcomp>
    pen = [pens[ci] for ci in self.__buffer[:, 2].astype(int)]
IndexError: list index out of range

-> On 3.3.10

Traceback (most recent call last):
  File "/Applications/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/Orange/canvas/scheme/widgetsscheme.py", line 822, in process_signals_for_widget
    handler(*args)
  File "/Applications/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/Orange/widgets/data/owpaintdata.py", line 1023, in set_data
    self.reset_to_input()
  File "/Applications/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/Orange/widgets/data/owpaintdata.py", line 1042, in reset_to_input
    self._replot()
  File "/Applications/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/Orange/widgets/data/owpaintdata.py", line 1227, in _replot
    pen=[pens[int(ci)] for ci in self.data[:, 2]]
  File "/Applications/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/Orange/widgets/data/owpaintdata.py", line 1227, in <listcomp>
    pen=[pens[int(ci)] for ci in self.data[:, 2]]
ValueError: cannot convert float NaN to integer

Description of changes

Includes

• Code changes
• Tests
• Documentation

[codecov-io]

Current coverage is 89.45% (diff: 100%)

Merging #1972 into master will not change coverage

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