WorkspaceFactory outputs invalid workspaces when child contains more spectra than parent

[DanNixon]

When creating a child workspace using the WorkspaceFactory where the child will have more spectra than the parent, no modification is done to the vertical axis, hence it ends up being too short for the child workspace which leads to issues if you try and do anything in Mantid the reads the axis.

When this happens the WorkspaceFactory should extend the axis and fill it with either zeros or empty strings to at least make it usable.

[DanNixon]

This issue was originally trac ticket 11882

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