Fix opening loc for an empty symbol

Author: maxprokopiev

src/prism.c

@@ -14205,7 +14205,6 @@ parse_strings(pm_parser_t *parser, pm_node_t *current) {
             // If we get here, then we have an end of a label immediately
             // after a start. In that case we'll create an empty symbol
             // node.
-            pm_token_t opening = not_provided(parser);
             pm_token_t content = parse_strings_empty_content(parser->previous.start);
             pm_symbol_node_t *symbol = pm_symbol_node_create(parser, &opening, &content, &parser->previous);
 

test/prism/location_test.rb

@@ -43,6 +43,7 @@ def test_ArrayPatternNode
     end
 
     def test_AssocNode
+      assert_location(AssocNode, "{ '': 1 }", 2...7) { |node| node.elements.first }
       assert_location(AssocNode, "{ foo: :bar }", 2...11) { |node| node.elements.first }
       assert_location(AssocNode, "{ :foo => :bar }", 2...14) { |node| node.elements.first }
       assert_location(AssocNode, "foo(bar: :baz)", 4...13) { |node| node.arguments.arguments.first.elements.first }