ZSQLCatalog: Use isIndexable from portal object directly

Required as preparation for migrating to ERP5 catalog which itself has an accessor
`isIndexable` which we plan to remain disabled all the time. So better to rely
directly on isIndexable from erp5 site object.

product/ZSQLCatalog/SQLCatalog.py

@@ -1288,7 +1288,7 @@ class Catalog(Folder,
       Similar problems may happen with relations and acquisition of uid values (ex. order_uid)
       with the risk of graph loops
     """
-    if not self.isIndexable():
+    if not self.getPortalObject().isIndexable():
       return None
 
     klass = self.__class__
@@ -1461,7 +1461,7 @@ class Catalog(Folder,
       LOG('ZSLQCatalog.SQLCatalog:catalogObjectList', WARNING,
           'idxs is ignored in this function and is only provided to be compatible with CMFCatalogAware.reindexObject.')
 
-    if not self.isIndexable():
+    if not self.getPortalObject().isIndexable():
       return
 
     # Reminder about optimization: It might be possible to issue just one
@@ -1710,7 +1710,7 @@ class Catalog(Folder,
     """
     Set the path as deleted
     """
-    if not self.isIndexable():
+    if not self.getPortalObject().isIndexable():
       return None
 
     if uid is None and path is not None:
@@ -1740,7 +1740,7 @@ class Catalog(Folder,
     XXX Add filter of methods
 
     """
-    if not self.isIndexable():
+    if not self.getPortalObject().isIndexable():
       return None
 
     if uid is None and path is not None: