btrfs: simplify last record detection at test_range_bit()

btrfs: simplify last record detection at test_range_bit()

The overflow detection for the start offset of the next record is not
really necessary, we can just stop iterating if the current record ends at
or after out end offset. This removes the need to test if the current
record end offset is (u64)-1 and to check if adding 1 to the current
end offset results in 0.

By testing only if the current record ends at or after the end offset, we
also don't need anymore to test the new start offset at the head of the
while loop.

This makes both the source code and assembly code simpler, more efficient
and shorter (reducing the object text size).

Also remove the pointless initialization to NULL of the state variable, as
we don't use it before the first assignment to it. This may help avoid
some warnings with clang tools such as the one reported/fixed by commit
966de47ff0c9 ("btrfs: remove redundant initialization of variables in
log_new_ancestors").

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>