coalesce function finds inconsistent column types in RasterJoin

[vpipkt]

As originally reported by @mjgolebiewski

https://gitter.im/locationtech/rasterframes?at=5f3e4d365d0f8f244081f87b

When doing raster join where left hand side table has a mix of Tile and ProjectedRasterTile, the variation in column type that coalesce finds causes an error.

[vpipkt]

@mjgolebiewski as soon as build passes I will go ahead and merge #500