[PATCH] git-tar-tree: fix write_trailer

[PATCH] git-tar-tree: fix write_trailer

write_trailer() writes the last 10k (a full block) of the tar archive.
write_if_needed() writes out a block *if* it is full and then sets
the offset to 0.  In nine out of ten cases the messed up write_trailer()
function didn't manage to fill the block thus not writing anything at
all, truncating the archive.  I was "lucky" to hit the other case and so
my testing ran OK.

Signed-off-by: Rene Scharfe <redacted>
Signed-off-by: Linus Torvalds <redacted>