Header modifications should preserve UTF-8 encoiding

Author: chibenwa

server/container/core/src/main/java/org/apache/james/server/core/InternetHeadersInputStream.java

@@ -69,7 +69,7 @@ private boolean readNextLine() {
             if (!headerLines.hasMoreElements()) {
                 line += LINE_SEPERATOR;
             }
-            currLine = line.getBytes(StandardCharsets.US_ASCII);
+            currLine = line.getBytes(StandardCharsets.UTF_8);
             return true;
         } else {
             return false;