Handle expansion errors during placeholder parsing - #1249

Personally, I feel like it's the responsibility of the expansion to properly handle and deal with exceptions.

From the PoV of PlaceholderAPI is it not expected for an expansion to throw anything on parse, but rather that this is handled gracefully and either a String or null being returned.
Having an expansion throw on parse, breaking the parsing tells me, that this is a failure on the expansion and that it should be reported to whoever made the expansion to get it fixed.

This genuinly feels like a band-aid solution to me.
Maybe PiggyPiglet or Funnycube think different tho.

Thanks for the feedback. I agree that an expansion should handle its own exceptions, but I think PlaceholderAPI still needs to treat expansion callbacks as a third-party boundary.

onRequest is called from CharsReplacer, and an unchecked exception currently aborts the entire parse. That means one broken expansion can prevent unrelated placeholders in the same string from being resolved; this is the failure described in #1107.

This change does not hide the failure: it logs the exception through the expansion logger, leaves the original placeholder unchanged (the same fallback used when no replacement is returned), and catches Exception rather than Error. The intent is containment, not replacing the need to fix the expansion itself.

Would you prefer a different logging or fallback behavior, or handling this at another layer?