Remove NaN weights. I do not know how this happens, and it seems to b…

…e very rare, but it did happen.

reproject/mosaicking/coadd.py

@@ -358,7 +358,7 @@ def reproject_and_coadd(
 
  # For the purposes of mosaicking, we mask out NaN values from the array
  # and set the footprint to 0 at these locations.
- reset = np.isnan(array)
+ reset = np.isnan(array) | np.isnan(weights)
  array[reset] = 0.0
  footprint[reset] = 0.0