generate_conditions() incorrectly subsetting data

[mkapur-noaa]

This does not affect the simulated_data example from the vignette, which only has a single break in each direction. The function needs to be updated to ensure that it breaks the data into domains bounded by the values in breakpoints; right now in the presence of two or more x or y breaks it is including all above/below. This might correspond to some dplyr back-compatibility issues identified elsewhere.