Fix return code for unknown controller buttons on linux controllers. Patch supplied by tctimmeh on JGO.

http://www.java-gaming.org/topics/updating-linux-stick-button-mappings/28838/view.html

plugins/linux/src/java/net/java/games/input/LinuxNativeTypesMap.java

@@ -841,7 +841,7 @@ class LinuxNativeTypesMap {
 			//ignore, pretend it was null
 		}
         if(retval == null) {
-            retval = Component.Identifier.Key.UNKNOWN;
+            retval = Component.Identifier.Button.UNKNOWN;
         }
         return retval;
     }