Cease randomized response generation when max channel capacity surpassed

This adds a small optimization for the costly randomized response
generation by moving the channel capacity limit check before creation.

Change-Id: I3a7f2197b139e1a6a7c4d6d8715bf93f6fabae03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401582


Reviewed-by: Andrew Paseltiner <apaseltiner@chromium.org>
Commit-Queue: Thomas Quintanilla <tquintanilla@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1279212}