pgsql: Take a little more care in set_backtrace().

Take a little more care in set_backtrace().

Coverity complained that the "errtrace" string is leaked if we return
early because backtrace_symbols fails. Another criticism that could
be leveled at this is that not providing any hint of what happened is
user-unfriendly. Fix that.

The odds of a leak here are small, and typically it wouldn't matter
anyway since the leak will be in ErrorContext which will soon get
reset. So I'm not feeling a need to back-patch.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5c8eda1f72a2b0a8c48ada9b872eb5ef581f7c81

Modified Files
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src/backend/utils/error/elog.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)