[ruby/irb] Fix Locale's encoding lookup for Japanese encodings

(https://github.com/ruby/irb/pull/568)

In 3ee79e89ad,
`encoding_aliases.rb` was introduced to return the correct encoding object for
`ujis` and `euc` encodings.

However, the return value of `@@legacy_encoding_alias_map[@encoding_name]`
is always overridden by a second look up with `Encoding.find(@encoding_name)`.
So the logic didn't work as expected.

This commit fixes the problem.

lib/irb/locale.rb

@@ -29,8 +29,9 @@ module IRB # :nodoc:
           begin load 'irb/encoding_aliases.rb'; rescue LoadError; end
           if @encoding = @@legacy_encoding_alias_map[@encoding_name]
             warn(("%s is obsolete. use %s" % ["#{@lang}_#{@territory}.#{@encoding_name}", "#{@lang}_#{@territory}.#{@encoding.name}"]), uplevel: 1)
+          else
+            @encoding = Encoding.find(@encoding_name) rescue nil
           end
-          @encoding = Encoding.find(@encoding_name) rescue nil
         end
       end
       @encoding ||= (Encoding.find('locale') rescue Encoding::ASCII_8BIT)

test/irb/test_locale.rb

@@ -31,7 +31,7 @@ module TestIRB
 
       assert_equal("ja", locale.lang)
       assert_equal("JP", locale.territory)
-      assert_equal("UTF-8", locale.encoding.name)
+      assert_equal(Encoding::EUC_JP, locale.encoding)
       assert_equal(nil, locale.modifier)
 
       assert_include $stderr.string, "ja_JP.ujis is obsolete. use ja_JP.EUC-JP"
@@ -47,7 +47,7 @@ module TestIRB
 
       assert_equal("ja", locale.lang)
       assert_equal("JP", locale.territory)
-      assert_equal("UTF-8", locale.encoding.name)
+      assert_equal(Encoding::EUC_JP, locale.encoding)
       assert_equal(nil, locale.modifier)
 
       assert_include $stderr.string, "ja_JP.euc is obsolete. use ja_JP.EUC-JP"