Merge branch 'jc/verify-loose-object-header'

Codepaths that read from an on-disk loose object were too loose in
validating what they are reading is a proper object file and
sometimes read past the data they read from the disk, which has
been corrected.  H/t to Gustavo Grieco for reporting.

* jc/verify-loose-object-header:
unpack_sha1_header(): detect malformed object header
streaming: make sure to notice corrupt object

diff --cc sha1_file.c
Simple merge

diff --cc streaming.c
Simple merge