cannot set custom smearing without data

[pkienzle]

To simulate a dataset before measurement, it would be useful to be able to set custom pinhole smear or custom slit smear even when there is no data available. When I try this I get

Traceback (most recent call last):
  File "/Users/pkienzle/Source/sasview-new/src/sas/sascalc/data_util/calcthread.py", line 268, in _run
    self.compute(*args, **kwargs)
ValueError: operands could not be broadcast together with shapes (0,) (49,) 

[butler]

verified on my windows — The log file has a bit longer of a traceback in some cases. Seems to have been introduced by Mathieu Doucet when adding the rescale functionality.

2016-10-06 21:12:22,845 ERROR Traceback (most recent call last):
  File "C:\Users\Paul\git\sasview_new\src\sas\sascalc\data_util\calcthread.py", line 268, in _run
    self.compute(*args, **kwargs)
  File "C:\Users\Paul\git\sasview_new\src\sas\sasgui\perspectives\fitting\model_thread.py", line 187, in compute
    / output[first_bin:last_bin+1]
ValueError: operands could not be broadcast together with shapes (0) (50) 

[mathieu]

In 286c7571e8019b4c28a92d3d497cac7da825076c/sasview:

Make sure we can compute models w/o data. Fixes #714