[backport#12951] [doc] Fix comment in FindForkInGlobalIndex
Summary:
[doc] Fix comment in FindForkInGlobalIndex (James O'Beirne)
Pull request description:
The comment erroneously implies that we're searching `chainActive` for the first block common to `locator`, but we're using the parameter `chain`.
Backport of Core PR12951
Test Plan:
just read it
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D7622