pgsql: Avoid memcpy() with same source and destination address.

Avoid memcpy() with same source and destination address.

The behavior of that is undefined, although unlikely to lead to problems in
practice.

Found by running regression tests with Valgrind.

Branch
------
REL8_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/ff9d757c67786b389f19abc3187d158adda500d8

Modified Files
--------------
src/backend/tsearch/dict_ispell.c |    9 ++++-----
src/backend/utils/adt/tsvector.c  |    3 ++-
2 files changed, 6 insertions(+), 6 deletions(-)