Bug in WaitForBackgroundWorkerShutdown() [REL9_5_STABLE]

Recently I've encountered a strange crash while calling elog(ERROR, "...") 
after the WaitForBackgroundWorkerShutdown() function. It turns out that 
_returns_ inside the PG_TRY()..PG_CATCH() block are *highly* undesirable, 
since they leave PG_exception_stack pointing to a local struct in a dead 
frame, which is an obvious UB. I've attached a patch which fixes this behavior 
in the aforementioned function, but there might be more errors like that 
elsewhere.

-- 
Dmitry Ivanov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company