merge-recursive: handle addition of submodule on our side of history

The code for a newly added path assumed that the path was a normal file, and thus checked for there being a directory still being in the way of the file. Note that since unpack_trees() does path-in-the-way checks already, the only way for there to be a directory in the way at this point in the code, is if there is some kind of D/F conflict in the merge. For a submodule addition on HEAD's side of history, the submodule would have already been present. This means that we do expect there to be a directory present but should not consider it to be "in the way"; instead, it's the expected submodule. So, when there's a submodule addition from HEAD's side, don't bother checking the working copy for a directory in the way. Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>