XXXMap.Entries.remove()
Removing an entry from the stash changes its order (the last entry will be copied to the current index).
Because the nextIndex is already set the iterator either loses some entries or, if already at the end of the map, returns invalid values.
Setting back the nextIndex to the currentIndex and advancing again should fix this.

This fixes #1299 for all map implementations.
remove test code.
Merge pull request #1312 from hneuer/objmapstash

XXXMap.Entries.remove()