[m-rev.] for review: check library install just once

[Julien Fischer]

On Wed, 12 Jan 2022, Zoltan Somogyi wrote:

> 2022-01-12 16:09 GMT+11:00 "Julien Fischer" <jfischer at opturion.com>:
>> We shouldn't be doing the check at all when building source file
>> mappings -- it's definitely a bug if we are.
>
> You just found the bug in my not-yet-finished change :-)

Not only that, I suspect I put the bug there in the first place ;-)

Julien.