FIX: re-order unit conversion and mask array coercion

closes matplotlib#19871

Author: tacaswell

lib/matplotlib/axes/_axes.py

@@ -5621,9 +5621,10 @@ def _pcolorargs(self, funcname, *args, shading='flat', **kwargs):
         if len(args) == 3:
             # Check x and y for bad data...
             C = np.asanyarray(args[2])
-            X, Y = [cbook.safe_masked_invalid(a) for a in args[:2]]
             # unit conversion allows e.g. datetime objects as axis values
+            X, Y = args[:2]
             X, Y = self._process_unit_info([("x", X), ("y", Y)], kwargs)
+            X, Y = [cbook.safe_masked_invalid(a) for a in [X, Y]]
 
             if funcname == 'pcolormesh':
                 if np.ma.is_masked(X) or np.ma.is_masked(Y):