Fix problems with raster overview factors
Fix problems with raster overview factors

Fixes #7082
Floating point used in division
Infinite results avoided
Negative powers avoided

CartoDB/cartodb,CartoDB/cartodb,splashblot/dronedb,splashblot/dronedb,splashblot/dronedb,CartoDB/cartodb,splashblot/dronedb,CartoDB/cartodb,splashblot/dronedb,CartoDB/cartodb