Minor bug in radmc3dPy dust mass calculations

[j6626]

In the getDustMass function in the data.py file in the radmc3dPy package, one has the option of either calculating the total dust mass or calculating the dust mass of individual species. The first code block, which calculates the dust mass of individual species, currently reads

        if idust > 0:
            #
            # I'm not sure if this is the right way of doing it but right now I don't have a better idea
            #
            if isinstance(self.grid, radmc3dOctree):
                dmass = (vol * self.rhodust[:, idust]).sum()
            else:
                dmass = (vol * self.rhodust[:, :, :, idust]).sum()

However, this does not allow calculation of the dust mass of species 0. The first line should be changed to something like if idust > -1 or if idust != -1 to get the intended behavior.