Don't fail the whole clone if you can't find a default branch

In commit 6bb35878 ("clone: set refs/remotes/origin/HEAD to default
branch when branch is specified, attempt 2") libgit2 was changed to set
the default remote branch when one was copied.

But it makes update_head_to_branch() return an error if the origin
doesn't even *have* a HEAD in the first place, since
git_remote_default_branch() will fail.

That's entirely wrong, and means that you cannot do "git_clone()" of a
particular branch on a remote repository when that remote doesn't have a
default branch at all.

So don't set the error code.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

src/libgit2/clone.c

@@ -282,7 +282,7 @@ static int update_head_to_branch(
 			reflog_message)) < 0)
 		goto cleanup;
 
-	if ((retcode = git_remote__default_branch(&default_branch, remote)) < 0)
+	if (git_remote__default_branch(&default_branch, remote) < 0)
 		goto cleanup;
 
 	if (!git_remote__matching_refspec(remote, git_str_cstr(&default_branch)))