Seek back to current filepos when mmap()ing with NO_MMAP
Seek back to current filepos when mmap()ing with NO_MMAP

"git-index-pack --fix-thin" relies on mmap() not changing the current
file position (otherwise the pack will be corrupted when writing the
final SHA1). Meet that expectation.

Signed-off-by: Johannes Schindelin <b4cf3b77c95aaa57254d96e276bf14cfc9472402@gmx.de>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git