test_unicode_normalize.rb: skip only once

* test/test_unicode_normalize.rb (setup): skip only once, and
  silently ignore other tests.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48388 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/test_unicode_normalize.rb

@@ -21,8 +21,6 @@ class TestUnicodeNormalize < Test::Unit::TestCase
         code_string.split(/\s/).collect { |cp| cp.to_i(16) }.pack('U*')
       end + [line[1]+1])
     end
-  rescue Errno::ENOENT => e
-    skip e.message
   end
 
   def to_codepoints(string)
@@ -31,6 +29,9 @@ class TestUnicodeNormalize < Test::Unit::TestCase
 
   def setup
     @@tests ||= read_tests
+  rescue Errno::ENOENT => e
+    @@tests ||= []
+    skip e.message
   end
 
   def self.generate_test_normalize(target, normalization, source, prechecked)