using a polygon with data.frame as grid produce errors in Summary

[aleruete]

Describe the bug
using a polygon with data.frame (e.g. reading a shape file) as grid produce errors in SummariseBirds, actually in includeUniqueSpillover(). This function Assumes that grid only has IDs in the data.frame an nothing else.

To Reproduce
Steps to reproduce the behavior:

1. Load a shape file with an attribute table with many columns
2. use it as grid in SummarizeBirds(..., sippover="unique") or overlay(.., spilover="unique") or BIRDS:::includeUniqueSpillOver()

Expected behavior
should interpret the grid in its various forms