Threading exception from live plotting and changes prompt font to black

Steps to reproduce

1. Run live plot (QtPlot). In this case, for debugging purposes, I ran the 1D loop example (https://github.com/QCoDeS/Qcodes/blob/master/docs/examples/Tutorial.ipynb) with live plotting and it throws a threading exception.
2. Live plot displays and runs correctly during data acquisition
3. After live plot ends upon sweep completion, Python throws an exception and changes to font to black in the anaconda prompt window.

Expected behaviour

The live plot should complete without throwing an exception. In some cases, the threading exception is thrown before the rest of the sequence can be completed.

Actual behaviour

The exception thrown is:

Exception in thread Thread-2:
Traceback (most recent call last):
  File "C:\Users\llamper\AppData\Local\Continuum\Anaconda3\envs\Python_3_5_ENV\lib\threading.py", line 914, in _bootstrap_inner
    self.run()
  File "C:\Users\llamper\AppData\Local\Continuum\Anaconda3\envs\Python_3_5_ENV\lib\site-packages\pyqtgraph\multiprocess\processes.py", line 469, in run
    cprint.cerr(self.color, line, -1)
  File "C:\Users\llamper\AppData\Local\Continuum\Anaconda3\envs\Python_3_5_ENV\lib\site-packages\pyqtgraph\util\cprint.py", line 100, in cerr
    cprint('stderr', *args)
  File "C:\Users\llamper\AppData\Local\Continuum\Anaconda3\envs\Python_3_5_ENV\lib\site-packages\pyqtgraph\util\cprint.py", line 79, in cprint
    kwds = WIN[arg]
KeyError: b'C:\\Users\\llamper\\AppData\\Local\\Continuum\\Anaconda3\\envs\\Python_3_5_ENV\\lib\\site-packages\\pyqtgraph\\graphicsItems\\PlotCurveItem.py:131: RuntimeWarning: All-NaN axis encountered\r\n'

Exception in thread Thread-1:
Traceback (most recent call last):
  File "C:\Users\llamper\AppData\Local\Continuum\Anaconda3\envs\Python_3_5_ENV\lib\threading.py", line 914, in _bootstrap_inner
    self.run()
  File "C:\Users\llamper\AppData\Local\Continuum\Anaconda3\envs\Python_3_5_ENV\lib\site-packages\pyqtgraph\multiprocess\processes.py", line 464, in run
    cprint.cout(self.color, line, -1)
  File "C:\Users\llamper\AppData\Local\Continuum\Anaconda3\envs\Python_3_5_ENV\lib\site-packages\pyqtgraph\util\cprint.py", line 96, in cout
    cprint('stdout', *args)
  File "C:\Users\llamper\AppData\Local\Continuum\Anaconda3\envs\Python_3_5_ENV\lib\site-packages\pyqtgraph\util\cprint.py", line 79, in cprint
    kwds = WIN[arg]
KeyError: b''

System

Win 10

Master

Reproduce the issue with QtPlot using docs/examples/Tutorial.ipynb and the 1D loop example on Windows. Start by examining the pyqtgraph multiprocess cprint paths shown in the traceback and the All-NaN warning from PlotCurveItem.py. Done means the sweep completes without threading exceptions and the Anaconda prompt font remains unchanged.