Fixed bug: When opening the overlay tool and we have a page without experimental data we get:

Traceback (most recent call last):
  File "/home/paul/repos/PyCorrFit/src/frontend.py", line 1209, in OnTool
    self.ToolsOpen[eid] = self.Tools[eid](self)
  File "/home/paul/repos/PyCorrFit/src/tools/selectcurves.py", line 78, in __init__
    curvedict, labels = self.GetCurvedict()
  File "/home/paul/repos/PyCorrFit/src/tools/selectcurves.py", line 102, in GetCurvedict
    curve = 1*Page.dataexp