Fix matfaust product M*F (with M a matrix and F a Faust).

(F'*M')' was handled correctly but not M*F (matrix on the left side).

It was raising this kind of error:
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Struct contents reference from a non-struct array object.

Error in matfaust.Faust/mtimes_trans (line 713)
                                if (F.isReal)

Error in * (line 657)
                                G = mtimes_trans(F, A, 0);
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