Check about change to MMitsubaElement

[DavidBrainard]

We had a problem where Mitsuba got unhappy because there was both a filename field and a value field in the place where spectral data go. I think this happened because some default got set up as a value and then we changed it by setting a filename.

To fix this, I added code to MMitsubaElement, line 76 ff, that checks to see if there is already a value or filename field, and removes this from the structure before adding a value or filename field back in. Doing this fixed our immediate problem, and in reading the code I don't see why it should break anything else, unless there are cases where one would want both fields. Since I don't know that such cases don't exist, I'm posting this question.

Here is the code (added code above the last two lines).

        % We don't want to end up with two fields in data, one a
        % value and one a filename -- we can have only one.  So, if
        % there already is something there, we clear it before
        % adding in below what we are supposed to be adding here.
        if isfield(property.data,'value')
            property.data = rmfield(property.data,'value');
        end
        if isfield(property.data,'filename')
            property.data = rmfield(property.data,'filename');
        end
        
        % Then do the adding in.
        property.setData(attributeName, value);
        property.type = type;

@benjamin-heasly If this edit seems OK, please so indicate and close. Otherwise let us know how we might better deal with this section. Thanks!