fallback env encoding to ASCII-8BIT

* hash.c (env_enc_str_new): as no locale/filesystem encoding is
  available in miniruby on Windows, fallback the encoding to
  ASCII-8BIT so it is valid encoding when the conversion failed.
  [ruby-core:89177] [Bug #15164]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64860 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

bootstraptest/test_env.rb

@@ -0,0 +1,12 @@
+assert_equal "true", %q{
+  ENV["ENVTEST"] = "\u{e9 3042 d76c}"
+  env = ENV["ENVTEST"]
+  env.valid_encoding?
+}
+
+# different encoding is used for PATH
+assert_equal "true", %q{
+  ENV["PATH"] = "\u{e9 3042 d76c}"
+  env = ENV["PATH"]
+  env.valid_encoding?
+}

hash.c

@@ -3360,7 +3360,7 @@ env_enc_str_new(const char *ptr, long len, rb_encoding *enc)
     rb_encoding *utf8 = rb_utf8_encoding();
     VALUE str = rb_enc_str_new(NULL, 0, (internal ? internal : enc));
     if (NIL_P(rb_str_cat_conv_enc_opts(str, 0, ptr, len, utf8, ecflags, Qnil))) {
-	rb_str_initialize(str, ptr, len, utf8);
+        rb_str_initialize(str, ptr, len, NULL);
     }
 #else
     VALUE str = rb_external_str_new_with_enc(ptr, len, enc);