Ensure non-Double types are boxed in expression function calls.

worldedit-core/src/main/java/com/sk89q/worldedit/internal/expression/Functions.java

@@ -75,6 +75,7 @@ public final class Functions {
             );
             handle = handle.asType(handle.type().changeReturnType(Number.class));
             handle = filterReturnValue(handle, DOUBLE_VALUE);
+            handle = handle.asType(handle.type().wrap());
         }
         // return vararg-ity
         if (wasVarargs) {