updated Tile get_cloudmasks function if not L1C nor L2C is present

sen2chain/tiles.py

@@ -306,12 +306,16 @@ class Tile:
             l1c_name = f.parent.name.replace("L2A_", "L1C_").replace("_USER_", "_OPER_") + ".SAFE"
             try:
                 date = self._products["l1c"][l1c_name].date
-                cloud_cover = self._products["l1c"][l1c_name].cloud_cover
+                cloud_cover = float(self._products["l1c"][l1c_name].cloud_cover)
             except KeyError:
                 date = Tile._get_date(f.parent.name)
-                cloud_cover = L2aProduct(f.parent.name, self.name).cloud_coverage_assessment
+                l2a = L2aProduct(f.parent.name, self.name)
+                if l2a.path.exists():
+                    cloud_cover = float(l2a.cloud_coverage_assessment)
+                else:
+                    cloud_cover = None
             self._products["cloudmasks"][f.name] = {"date": date, 
-                                                            "cloud_cover": float(cloud_cover), 
+                                                            "cloud_cover": cloud_cover, 
                                                             #~ "version": re.findall(r"_(CM...)", f.name)[0]
                                                             }