pgsql: Call SetLastError(0) before calling the file mapping functions to

Log Message:
-----------
Call SetLastError(0) before calling the file mapping functions
to make sure that the error code is reset, as a precaution in
case the API doesn't properly reset it on success. This could
be necessary, since we check the error value even if the function
doesn't fail for specific success cases.

Tags:
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REL8_3_STABLE

Modified Files:
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pgsql/src/backend/port:
win32_shmem.c (r1.4.2.2 -> r1.4.2.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/port/win32_shmem.c?r1=1.4.2.2&r2=1.4.2.3)