Fix handling "rescue" inside paren

The parse_rescue method detects the end of class list for catch,
but it doesn't support postfix rescue inside paren.
This commit fixes it.

Author: aycabta

lib/rdoc/parser/ruby.rb

@@ -1588,6 +1588,7 @@ def parse_require(context, comment)
   def parse_rescue
     skip_tkspace false
 
+    nest = 0
     while tk = get_tk
       case tk
       when TkNL, TkSEMICOLON then
@@ -1596,6 +1597,11 @@ def parse_rescue
         skip_tkspace false
 
         get_tk if TkNL === peek_tk
+      when TkLPAREN, TkfLPAREN then
+        nest += 1
+      when TkRPAREN then
+        nest -= 1
+        break if nest < 0
       end
 
       skip_tkspace false