Fix mishandling of memcache error

[t3-aoki]

When memcache.SetMulti() returns appengine.MultiError in following part, nds.putMulti() returns nil as []*datastore.Key.

nds/put.go

Lines 157 to 160 in de1d21b

	} else if err := memcacheSetMulti(memcacheCtx,
	lockMemcacheItems); err != nil {
	return nil, err
	}

It causes a panic (index out of range) in following part of nds.PutMulti() because it makes putKey[i] nil.

nds/put.go

Line 79 in de1d21b

groupedKeys[lo+j] = putKeys[i][j]

This PR will fix the issue in v1.
I think there is same bug in v2.

[coveralls]

Coverage remained the same at 100.0% when pulling 2bf4eed on t3-aoki:fix-mishandling-of-memcache-error into 304641c on qedus:master.

[jongillham]

Thank you very much for this! I'll have a look and merge.

Any idea why go.mod and go.sum have so many extra dependencies with this update?

[t3-aoki]

@jongillham Thank you for your comment.

Any idea why go.mod and go.sum have so many extra dependencies with this update?

Sorry for lack of the information. The aetest broken since gcloud v265.0.0, so I had to update golang/appengine to fix it.
Please refer:
golang/appengine#214