Cannot use scalar value as an array

There are a couple of issues in the queue that were describing some more complex problems, and part of those problems had this issue within them. The error that was reported (and I am seeing) is some php warnings of this kind:

The overall issue I believe were fixed #369020: "Every First Saturday" skips Feb, March and #409476: date_timezone_set() & date_format() error when editing CCK date repeating fields., but no one seemed to notice that the scalar value warning was a bit separate (or at least I assume so).

I found that date_field's $items are more that just a 'value' and 'rrule' and in some cases are not even arrays yet. This is what causes those scalar warnings. The attached patch simply check to make sure that the $additions[$field['field_name']][$delta] is an array before treating it as such. Hopefully this is not actually a deeper issue and this check is simply sweeping the dirt under the rug.