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
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/c7a186e392d4654148a45eaf8ffbf026553ecbdb

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