model.numdlb export should always write file name strings as "model"

[ThatNintendoNerd]

When exporting a model as .numdlb with a different inputted file name other than model writes that file name in-place of model. For instance, naming your .numdlb file ikemodel will produce this within the model.numdlb. To my knowledge, every .numdlb file is named model, so regardless of the file name inputted upon export, the file name string should always be kept as model.