Move return statements out of PG_TRY blocks.

 Move return statements out of PG_TRY blocks.
 
 If we exit a PG_TRY block early via "continue", "break", "goto", or
 "return", we'll skip unwinding its exception stack.  This change
 moves a couple of such "return" statements in PL/Python out of
 PG_TRY blocks.  This was introduced in d0aa965c0a and affects all
 supported versions.
 
 We might also be able to add compile-time checks to prevent
 recurrence, but that is left as a future exercise.
 
 Reported-by: Mikhail Gribkov, Xing Guo
 Author: Xing Guo
 Reviewed-by: Michael Paquier, Andres Freund, Tom Lane
 Discussion: https://postgr.es/m/CAMEv5_v5Y%2B-D%3DCO1%2Bqoe16sAmgC4sbbQjz%2BUtcHmB6zcgS%2B5Ew%40mail.gmail.com
 Discussion: https://postgr.es/m/CACpMh%2BCMsGMRKFzFMm3bYTzQmMU5nfEEoEDU2apJcc4hid36AQ%40mail.gmail.com
 Backpatch-through: 11 (all supported versions)