Redo of matrix->normalize with a multiplication factor doesn't reproduce data

1. Have a spectrum
2. Matrix -> Normalize with a multiplication factor (say: 2). Check the Y-axis for the peak intensities
3. Undo
4. Redo. Check the Y axis. Y axis is now 4x larger than in step 2

Reason: not properly inverted in self.undoList.append(lambda self: self.normalize(1.0 / mult, scale, ftype, axis, select=select))

Note: Multiplication in the UI refers to variable scale, not mult. Just to keep life simple :)