crypto: fix randomInt bias

[tniessen]

@puzpuzpuz found this issue in #35110 (comment). Opening a separate PR to make sure this fix can land and be backported quickly, if necessary.

This patch also changes a few comments and definitions to make the necessary conditions easier to understand.

The actual effect of this bias is small, but the mere existence of bias defeats the purpose of this function.

Refs: #34600

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35470/

Infrastructure failure:

16:41:06 FATAL: Server returned HTTP response code: 502 for URL: https://raw.githubusercontent.com/nodejs/build/master/jenkins/scripts/VersionSelectorScript.groovy?a
16:41:06 java.io.IOException: Server returned HTTP response code: 502 for URL: https://raw.githubusercontent.com/nodejs/build/master/jenkins/scripts/VersionSelectorScript.groovy?a

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35471/

Infrastructure failure:

16:42:04 + bash -ex -s before
16:42:04 + curl https://raw.githubusercontent.com/nodejs/build/master/jenkins/scripts/node-test-commit-pre.sh
16:42:04 % Total % Received % Xferd Average Speed Time Time Time Current
16:42:04 Dload Upload Total Spent Left Speed
16:42:04 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
100 18 100 18 0 0 86 0 --:--:-- --:--:-- --:--:-- 87
16:42:04 + connection failure
16:42:04 bash: line 1: connection: command not found
16:42:04 Build step 'Execute shell' marked build as failure

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35473/

[tniessen]

The asan failure seems related to #36779 and is unrelated to this change.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35541/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35542/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/35544/ (✅)

[tniessen]

Landed in 4db9854, thanks for reviewing.