pgsql: Silence minor compiler warnings.

Silence minor compiler warnings.

Depending on compiler version and optimization level, we might
get a complaint that lazy_scan_heap's "freespace" is used
uninitialized.

Compilers not aware that ereport(ERROR) doesn't return complained
about bbsink_lz4_new().

Assigning "-1" to a uint64 value has unportable results; fortunately,
the value of xlogreadsegno is unimportant when xlogreadfd is -1.
(It looks to me like there is no need for xlogreadsegno to be static
in the first place, but I didn't venture to change that.)

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/302612a6c74fb16f26d094ff47e9c59cf412740c

Modified Files
--------------
src/backend/access/heap/vacuumlazy.c | 2 +-
src/backend/replication/basebackup_lz4.c | 1 +
src/bin/pg_rewind/parsexlog.c | 2 +-
3 files changed, 3 insertions(+), 2 deletions(-)