Update glob left brace detection to handle escaped backslash case

Author: bjfish

spec/ruby/core/dir/fixtures/common.rb

@@ -92,6 +92,7 @@ def self.mock_dir_files
           special/|
 
           special/こんにちは.txt
+          special/\a
         ]
       end
     end

spec/ruby/core/dir/shared/glob.rb

@@ -80,6 +80,10 @@
     it "matches regexp special |" do
       Dir.send(@method, 'special/|').should == ['special/|']
     end
+
+    it "matches files with backslashes in their name" do
+      Dir.glob('special/\\\\{a,b}').should == ['special/\a']
+    end
   end
 
   it "matches regexp special ^" do

src/main/ruby/truffleruby/core/dir_glob.rb

@@ -455,7 +455,8 @@ def self.glob(base_dir, pattern, flags, matches)
         return matches
       end
 
-      left_brace_index = pattern.index(/(?<!\\){/)
+      left_brace_match = pattern.match(/(\\*)(\{)/)
+      left_brace_index = left_brace_match && left_brace_match[1].size.even? ? left_brace_match.begin(2) : nil
       if left_brace_index
         patterns = compile(pattern, left_brace_index, flags)