qfbpowraw(Qfb(5, 2, 5),-1) --> wrong result

[Bill Allombert <allomber@math.u-bordeaux.fr>]

Hello PARI-dev,

? qfbpowraw(Qfb(5, 2, 5),-1)
%1 = Qfb(5, 2, 5)

Which is false, it should be Qfb(5, -2, 5).

The bug stem from the fact that ginv() is called
when ginv() want to reduce the form.

Cheers,
Bill.