Fix SWCommandUtils.numberMapper with nan

SpigotCore_Main/src/de/steamwar/command/SWCommandUtils.java

@@ -261,6 +261,9 @@ public class SWCommandUtils {
     private static <T> Function<String, T> numberMapper(Function<String, T> mapper) {
         return s -> {
             try {
+                if (s.equalsIgnoreCase("nan")) {
+                    return null;
+                }
                 return mapper.apply(s);
             } catch (NumberFormatException e) {
                 return null;