WG of CurCell can fail

[mkromberg]

I do not have a current repro, but in the OWUM application, the following was observed at least once:

T: #5: {"WG":{"ID":"F1.TC.Work.GRID","Properties":["CurCell"],"WGID":"50"}}
R: #5: {"WG":{"ID":"F1.TC.Work.GRID","Properties":{},"WGID":"50"}}

WG of CurCell on a grid should always succeed, and always return a value which is "within" the shape of the Values property. In other words, if Values is reduced in size, CurCell should be adjusted.