BugFix: SliceAlgorithmDialog sends incorrect dimension information

[AntonPiccardoSelg]

'''To reproduce:'''

1. Load two event MD event workspaces into MantidPlot of which one has three dimensions and the other has four dimensions.
2. Execute the BinMD algorithm. The BinMD algorithm dialog will appear.
3. Load the four-dim workspace and bin it.
4. Execute the BinMD algorithm. The BinMD algorithm dialog will appear.
5. Load the three-dim workspace and bin it.
6. You shoud see an error message.

The dialog memorises the strucutre of the workspace which was loaded last. When you load the four-dim workspace it creates a dimension property which is four-dim. Then when we switch to a three-dim workspace the last dimsion structure is not flushed from the dimension property

[AntonPiccardoSelg]

This issue was originally trac ticket 10959

[AntonPiccardoSelg]

http://trac.mantidproject.org/mantid/raw-attachment/ticket/10959/MDEvent1.nxs
(uploaded by @picatess on 2015-01-27T11:49:53)

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