fix mask check

pypeit/find_objects.py

@@ -1184,10 +1184,12 @@ def joint_skysub(self, skymask=None, update_crmask=True, trim_edg=(0,0),
             counts = global_sky
             _scale = None if self.sciImg.img_scale is None else self.sciImg.img_scale[thismask]
             # NOTE: darkcurr must be a float for the call below to work.
-            var = procimg.variance_model(self.sciImg.base_var[thismask], counts=counts[thismask],
-                                         count_scale=_scale, noise_floor=adderr)
-            model_ivar[thismask] = utils.inverse(var)
-
+            if not self.bkg_redux:
+                var = procimg.variance_model(self.sciImg.base_var[thismask], counts=counts[thismask],
+                                             count_scale=_scale, noise_floor=adderr)
+                model_ivar[thismask] = utils.inverse(var)
+            else:
+                model_ivar[thismask] = self.sciImg.ivar[thismask]
             # RJC :: Recalculating the global sky and flexure is probably overkill... but please keep this code in for now
             # Recalculate the sky on each individual slit and redetermine the spectral flexure
             # global_sky_sep = super().global_skysub(skymask=skymask, update_crmask=update_crmask,
@@ -1227,7 +1229,8 @@ def global_skysub(self, skymask=None, update_crmask=True, trim_edg=(0,0),
         global_sky_sep = super().global_skysub(skymask=skymask, update_crmask=update_crmask,
                                                trim_edg=trim_edg, show_fit=show_fit, show=show,
                                                show_objs=show_objs)
-        if np.any(global_sky_sep[skymask] == 0):
+        # Check if any slits failed
+        if np.any(global_sky_sep[self.slitmask>=0] == 0) and not self.bkg_redux:
             # Cannot continue without a sky model for all slits
             msgs.error("Global sky subtraction has failed for at least one slit.")