parse.y: Fix locations of none and mid-rule actions

When an empty rule or a mid-rule action is reduced,
`YYLLOC_DEFAULT` is called with the third parameter to be zero.
If we use `RUBY_SET_YYLLOC_OF_NONE` to set their locations,
sometimes the end position of NODE indicates a blank.
For example, `a.b ;` generates `NODE_CALL (line: 1, location: (1,0)-(1,4))*`,
whose end position indicates a blank.

This is because of the following reasons:

* `NODE_CALL` is created when `primary_value call_op operation2 opt_paren_args` is
  reduced to `method_call`.
* `opt_paren_args` is `none`.
* `yylex` is called and `lex.pbeg` moves before `none` is reduced, so
  the beginning position of `none` does not match with the end position of `operation2`.

To fix locations, use `YYRHSLOC(Rhs, 0)` in `YYLLOC_DEFAULT`
(0 "refers to the symbol just before the reduction").

By this change, the bottom of the location stack would be referenced,
so initialize the bottom with `RUBY_SET_YYLLOC_OF_NONE` in `%initial-action`.

Ref: https://www.gnu.org/software/bison/manual/html_node/Location-Default-Action.html#Location-Default-Action

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63623 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

parse.y

@@ -59,7 +59,10 @@
 	  (Current).end_pos = YYRHSLOC(Rhs, N).end_pos;			\
 	}								\
       else								\
-	RUBY_SET_YYLLOC_OF_NONE(Current);				\
+        {                                                               \
+          (Current).beg_pos = YYRHSLOC(Rhs, 0).end_pos;                 \
+          (Current).end_pos = YYRHSLOC(Rhs, 0).end_pos;                 \
+        }                                                               \
     while (0)
 
 #define RUBY_SET_YYLLOC_FROM_STRTERM_HEREDOC(Current)			\
@@ -747,6 +750,10 @@ static void token_info_warn(struct parser_params *p, const char *token, token_in
 %pure-parser
 %lex-param {struct parser_params *p}
 %parse-param {struct parser_params *p}
+%initial-action
+{
+    RUBY_SET_YYLLOC_OF_NONE(@$);
+};
 
 %union {
     VALUE val;