defrag.f2fs: fix not to allocate current segment
defrag.f2fs: fix not to allocate current segment

This patch fixes allocating wrong segment which has zero data but is registered
as a current segment.

Change-Id: I863301e1243038420d877b7d7a74160b80810ecb
Signed-off-by: Jaegeuk Kim <71255387a32c360dfbe6dfb7aaeb123bf1dc8cb6@kernel.org>

TeamTwisted/android_external_f2fs-tools,TeamTwisted/android_external_f2fs-tools