Merge pull request #520 from iweiss/UNDERTOW-1091

[UNDERTOW-1091] Invalid response code for empty host value in request

Author: fl4via

core/src/main/java/io/undertow/server/HttpServerExchange.java

@@ -622,7 +622,7 @@ private String extractCharset(HeaderMap headers) {
      */
     public String getHostName() {
         String host = requestHeaders.getFirst(Headers.HOST);
-        if (host == null) {
+        if (host == null || "".equals(host.trim())) {
             host = getDestinationAddress().getHostString();
         } else {
             if (host.startsWith("[")) {