Add `Entry#zip64?` as a better way detect Zip64 entries.

lib/zip/central_directory.rb

@@ -47,7 +47,7 @@ module Zip
       if ::Zip.write_zip64_support
         need_zip64_eocd = cdir_offset > 0xFFFFFFFF || cdir_size > 0xFFFFFFFF \
                           || @entry_set.size > 0xFFFF
-        need_zip64_eocd ||= @entry_set.any? { |entry| entry.extra['Zip64'] }
+        need_zip64_eocd ||= @entry_set.any?(&:zip64?)
         if need_zip64_eocd
           write_64_e_o_c_d(io, cdir_offset, cdir_size)
           write_64_eocd_locator(io, eocd_offset)
@@ -185,7 +185,7 @@ module Zip
         entry = Entry.read_c_dir_entry(io)
         next unless entry
 
-        offset = if entry.extra['Zip64']
+        offset = if entry.zip64?
                    entry.extra['Zip64'].relative_header_offset
                  else
                    entry.local_header_offset

lib/zip/entry.rb

@@ -154,6 +154,10 @@ module Zip
       @compression_method = (@ftype == :directory ? STORED : method)
     end
 
+    def zip64?
+      !@extra['Zip64'].nil?
+    end
+
     def file_type_is?(type)
       raise InternalError, "current filetype is unknown: #{inspect}" unless @ftype
 
@@ -721,7 +725,7 @@ module Zip
     # apply missing data from the zip64 extra information field, if present
     # (required when file sizes exceed 2**32, but can be used for all files)
     def parse_zip64_extra(for_local_header) #:nodoc:all
-      return if @extra['Zip64'].nil?
+      return unless zip64?
 
       if for_local_header
         @size, @compressed_size = @extra['Zip64'].parse(@size, @compressed_size)

test/local_entry_test.rb

@@ -122,13 +122,13 @@ class ZipLocalEntryTest < MiniTest::Test
     buf1 = StringIO.new
     entry = ::Zip::Entry.new('file.zip', 'entry_name')
     entry.write_local_entry(buf1)
-    assert(entry.extra['Zip64'].nil?, 'zip64 extra is unnecessarily present')
+    refute(entry.zip64?, 'zip64 extra is unnecessarily present')
 
     buf2 = StringIO.new
     entry.size = 0x123456789ABCDEF0
     entry.compressed_size = 0x0123456789ABCDEF
     entry.write_local_entry(buf2, rewrite: true)
-    refute_nil(entry.extra['Zip64'])
+    assert(entry.zip64?)
     refute_equal(buf1.size, 0)
     assert_equal(buf1.size, buf2.size) # it can't grow, or we'd clobber file data
   end