Trac links are automatically added even when `#NNN` reference has an existing link

[danielbachhuber]

Given post content like:

For instance, consider the following (<a href="https://github.com/wp-cli/wp-cli/issues/2523">from #2523</a>):

P2 will transform the HTML to the following:

For instance, consider the following (<a href="https://github.com/wp-cli/wp-cli/issues/2523">from </a><span class="p2_hovercardify"><a href="https://core.trac.wordpress.org/ticket/2523" class="nocard">#2523</a></span>):

I'd expect my issue reference to be ignored when it already has a link.

[obenland]

#2602 was marked as a duplicate.