tweaks to catch in AsyncProcessorHelper::executeRequest
tweaks to catch in AsyncProcessorHelper::executeRequest

Summary:
* Use a catch-all clause to catch anything that could be thrown, not just some things that could be thrown.
* Log the type of the caught object in addition to any message.
* Remove an unused `exception_wrapper` instance.
* Remove a redundant `return;` statement at the end of the function.

Reviewed By: roddym

Differential Revision: D40011239

fbshipit-source-id: d1bd295b7284077bb8e0c311642001ada88016e8

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