encoding an invalid utf-8 to utf-8 does not trigger ":invalid => :rep…

…lace". when it happens, we need to hop to utf-16le then back to utf-8

lib/mail/version_specific/ruby_1_9.rb

@@ -54,7 +54,8 @@ def Ruby19.b_value_decode(str)
         str = Ruby19.decode_base64(match[2])
         str.force_encoding(fix_encoding(encoding))
       end
-      str.encode("utf-8", :invalid => :replace, :replace => "") 
+      decoded = str.encode("utf-8", :invalid => :replace, :replace => "")
+      decoded.valid_encoding? ? decoded : decoded.encode("utf-16le", :invalid => :replace, :replace => "").encode("utf-8")
     end
 
     def Ruby19.q_value_encode(str, encoding = nil)
@@ -69,7 +70,8 @@ def Ruby19.q_value_decode(str)
         str = Encodings::QuotedPrintable.decode(match[2])
         str.force_encoding(fix_encoding(encoding))
       end
-      str.encode("utf-8", :invalid => :replace, :replace => "") 
+      decoded = str.encode("utf-8", :invalid => :replace, :replace => "")
+      decoded.valid_encoding? ? decoded : decoded.encode("utf-16le", :invalid => :replace, :replace => "").encode("utf-8")
     end
 
     def Ruby19.param_decode(str, encoding)

spec/mail/encoding_spec.rb

@@ -186,4 +186,9 @@
     mail.parts[0].content_type.should == "text/html; charset=ISO-8859-1"
   end
 
+  it "should skip invalid characters" do
+    m = Mail.new
+    m['Subject'] = Mail::SubjectField.new("=?utf-8?Q?Hello_=96_World?=")
+    lambda { m.subject.should be_valid_encoding }.should_not raise_error
+  end
 end