-gpu flag does not work with multiple input files

[JLeliaert]

When using multiple input files in combination with the "-gpu" flag, mumax3 distributes the input files over all gpu's instead of only the one specified.

e.g. mumax3 -gpu=1 input1.mx3 input2.mx3

results in

mumax3 [-gpu=0 -http=:35368 input1.mx3]
mumax3 [-gpu=1 -http=:35369 input2.mx3]

whereas the expected behaviour would be that both input files would run serially only on gpu=1