regression: git push in non-shared repo stalls (v2.11.0+)

Hi,

I observe a regression that seems to have been introduced between v2.10.0 and v2.11.0. When I try to push into a repository on the local filesystem that belongs to another user and has not explicitly been prepared for shared use, v2.11.0 shows some of the usual diagnostic output and then freezes instead of announcing why it failed to push.

Horst

Steps to reproduce (tested on Debian 8 "Jessie" amd64):
 -  User A creates a bare repository:
    mkdir /tmp/gittest
    git init --bare /tmp/gittest
 -  User B clones it, adds and commits a file:
    git clone /tmp/gittest
    cd gittest
    echo 42 > x
    git add x
    git commit -m test
 -  User B tries to push to user A's bare repo:
    git push

Expected result (git v2.10.0 and earlier):
test@ios:~/gittest$ git push
Counting objects: 3, done.
Writing objects: 100% (3/3), 230 bytes | 0 bytes/s, done.
Total 3 (delta 0), reused 0 (delta 0)
remote: error: insufficient permission for adding an object to repository database objects
remote: fatal: failed to write object
error: unpack failed: unpack-objects abnormal exit
To /tmp/gittest
 ! [remote rejected] master -> master (unpacker error)
error: failed to push some refs to '/tmp/gittest'

Actual result (git v2.11.0, v2.12.0, and 2.12.0.189.g3bc53220c): test@ios:~/gittest$ git push Counting objects: 3, done. Writing objects: 100% (3/3), 230 bytes | 0 bytes/s, done. Total 3 (delta 0), reused 0 (delta 0) [... git freezes here ...]