[Bug #18962] Do not read again once reached EOF

`Ripper::Lexer#parse` re-parses the source code with syntax errors
when `raise_errors: false`.

Co-Authored-By: tompng <tomoyapenguin@gmail.com>

parse.y

@@ -9299,6 +9299,7 @@ parser_yylex(struct parser_params *p)
       case '\004':		/* ^D */
       case '\032':		/* ^Z */
       case -1:			/* end of script. */
+	p->eofp  = 1;
 	return 0;
 
 	/* white spaces */

test/ripper/test_lexer.rb

@@ -100,6 +100,20 @@ class TestRipper::Lexer < Test::Unit::TestCase
     assert_equal expect, Ripper.lex(src).map {|e| e[1]}
   end
 
+  def test_end_of_script_char
+    all_assertions do |all|
+      ["a", %w"[a ]", %w"{, }", "if"].each do |src, append|
+        expected = Ripper.lex(src).map {|e| e[1]}
+        ["\0b", "\4b", "\32b"].each do |eof|
+          c = "#{src}#{eof}#{append}"
+          all.for(c) do
+            assert_equal expected, Ripper.lex(c).map {|e| e[1]}
+          end
+        end
+      end
+    end
+  end
+
   def test_slice
     assert_equal "string\#{nil}\n",
       Ripper.slice(%(<<HERE\nstring\#{nil}\nHERE), "heredoc_beg .*? nl $(.*?) heredoc_end", 1)