7471: Fix python3 sort key errors

Ensure input to strxfrm is correct type.
Apply patch by Marc Hulsman.

gramps/gen/utils/grampslocale.py

@@ -852,12 +852,12 @@ class GrampsLocale(object):
             #ICU can digest strings and unicode
             return self.collator.getCollationKey(string).getByteArray()
         else:
+            if sys.version_info[0] < 3 and isinstance(string, unicode):
+                string = string.encode("utf-8", "replace")
+            if sys.version_info[0] >= 3 and isinstance(string, bytes):
+                string = string.decode("utf-8", "replace")
             try:
-                if sys.version_info[0] < 3 and isinstance(string, unicode):
-                    key = locale.strxfrm(string.encode("utf-8", "replace"))
-                else:
-                    key = locale.strxfrm(string)
-
+                key = locale.strxfrm(string)
             except Exception as err:
                 LOG.warn("Failed to obtain key for %s because %s",
                          self.collation, str(err))

gramps/gui/views/treemodels/treebasemodel.py

@@ -92,10 +92,10 @@ class Node(object):
             #sortkey must be localized sort, so 
             self.sortkey = glocale.sort_key(sortkey)
             if not self.sortkey:
-                self.sortkey = b''
+                self.sortkey = glocale.sort_key('')
         else:
             self.name = ''
-            self.sortkey = b''
+            self.sortkey = glocale.sort_key('')
         self.ref = ref
         self.handle = handle
         self.secondary = secondary