In general, fixing corrupt objects can be pretty difficult. However, in this case, we're confident that the problem is an aborted transfer, meaning that the object is in a remote repository, so we should be able to safely remove our copy and let git get it from the remote, correctly this time.
The temporary object file, with zero size, can obviously just be removed. It's not going to do us any good. The corrupt object which refers to it, d4a0e75..., is our real problem. It can be found in .git/objects/d4/a0e75.... As I said above, it's going to be safe to remove, but just in case, back it up first.
At this point, a fresh git pull should succeed.
...assuming it was going to succeed in the first place. In this case, it appears that some local modifications prevented the attempted merge, so a stash, pull, stash pop was in order. This could happen with any merge, though, and didn't have anything to do with the corrupted object. (Unless there was some index cleanup necessary, and the stash did that in the process... but I don't believe so.)