pgsql: Fix poorly thought-through code from commit 5c3c3cd0a3046339.

Fix poorly thought-through code from commit 5c3c3cd0a3046339.

It's not entirely clear to me whether PyString_AsString can return
null (looks like the answer might vary between Python 2 and 3).
But in any case, this code's attempt to cope with the possibility
was quite broken, because pstrdup() neither allows a null argument
nor ever returns a null.

Moreover, the code below this point assumes that "message" is a
palloc'd string, which would not be the case for a dgettext result.

Fix both problems by doing the pstrdup step separately.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/f73b2bbbdcb387aa90ff619fe03d1924ed82b868

Modified Files
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src/pl/plpython/plpy_plpymodule.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)