crecord: add a default regex to curseschunkselector

Whether there is a regex to search or not will affect if we can find
the next or the previous search hit.

mercurial/crecord.py

@@ -709,6 +709,8 b' class curseschunkselector:'
             )
         self.operation = operation
 
+        self.regex = None
+
     def uparrowevent(self):
         """
         try to select the previous item to the current item that has the