Don't try to ReParameter symbols not in the group

[aconty]

Sometimes, after optimization, symbols tagged as interactive get removed because they are unused. But ReParameter is failing with errors because it goes looking for the removed symbol to master, which is, of course, not interactive. This patch avoids that so the symbol is not found, and then we just return false.

Description

We found this issue in production because code was being removed, then symbols too, then reparameter failed. There is no other way to prevent the error than from inside OSL. I'm suggesting this change but any other way to handle it would work for us.

Checklist:

• [x] I have read the contribution guidelines.
• [x] I have previously submitted a Contributor License Agreement.
• [x] I have updated the documentation, if applicable.
• [x] I have ensured that the change is tested somewhere in the testsuite (adding new test cases if necessary).
• [x] My code follows the prevailing code style of this project.