fix the fetches-per-server quota calculation

since commit bad5a523, when the fetches-per-server quota was increased or decreased, instead of the value being set to the newly calculated quota, it was set to the minimum of the new quota or 1 - which effectely meant it was always set to 1. it should instead have been the maximum, to prevent the value from ever dropping to zero.

Closes #3327 (closed)