Recent change to resonator analysis class breaks circle fit in 2D Measurements.

[thilokru]

See comment https://github.com/qkitgroup/qkit/commit/c93b1c6d94d7858e67a519b58e455d7daea146c9#r115820757 . Setting i=1 at the beginning of the loop fixes the problem, but this an ugly hack.

@Schneider1