[1.6.x] Fixed #22565 -- Prevented pgettext_lazy crash with bytestring input

Thanks ygbo for the report.
Backport of 142c27218 from master.

django/utils/translation/trans_real.py

@@ -285,7 +285,8 @@ def pgettext(context, message):
     result = ugettext(msg_with_ctxt)
     if CONTEXT_SEPARATOR in result:
         # Translation not found
-        result = message
+        # force unicode, because lazy version expects unicode
+        result = force_text(message)
     return result
 
 def gettext_noop(message):