fix bug affecting almost empty files

--HG--
branch : pmacs2

lex3.py

@@ -253,12 +253,13 @@ class RegionRule(Rule):
             # ok, so now loop over all the tokens in the current grammar, until
             # the stop-token (if any) is found, and return each result as we get
             # it.
+            tok = None
             for tok in self._lex(lexer, toresume, tokname, stopre, grammar):
                 yield tok
 
             # ok, so now either we found the stop-token, and have a new parent
             # for future tokens (if any), or we are done.
-            if tok.name == tokname:
+            if tok is not None and tok.name == tokname:
                 toresume = [tok]
                 matchd.update(tok.matchd)
             else: