fix(core): catch missing reduced costs and shadow prices.

[Palaract]

This simple code change in the get_solution function in core/solution.py catches all exceptions regarding reduced costs and shadow prices not being available. If the latest change in the downstream dependency optlang (https://github.com/opencobra/optlang/pull/259) is used here, then the general exception can be replaced with a ValueError which would be more specific and still solver agnostic. Still, Exception should catch GurobiErrors as well as ValueErrors and only in the case where those RC and Pi variables are actually accessed, therefore I don't deem it problematic if it would stay like that.

I ran the tests via tox and also tested both minimal working examples of issue numbers #1381 and #1372, both are now working just fine.

• [x] fix #1381
• [x] fix #1372
• [x] description of fix
• [x] tests passed
• [x] add an entry to the next release

[Palaract]

I hope this is concise and correct enough! Thank you for looking into this :)