GUACAMOLE-422: Only send timezone if it's there.

guacamole-common/src/main/java/org/apache/guacamole/protocol/ConfiguredGuacamoleSocket.java

@@ -185,12 +185,15 @@ public class ConfiguredGuacamoleSocket implements GuacamoleSocket {
                     info.getImageMimetypes().toArray(new String[0])
                 ));
         
-        // Send client timezone
+        // Send client timezone, if available
+        String timezone = info.getTimezone();
+        if (timezone != null && !timezone.isEmpty()) {
             writer.writeInstruction(
                     new GuacamoleInstruction(
                         "timezone",
                         info.getTimezone()
                     ));
+        }
 
         // Send args
         writer.writeInstruction(new GuacamoleInstruction("connect", arg_values));