mruby-enum-ext: filter_map should not ignore index; fix #6504

mrbgems/mruby-enum-ext/mrblib/enum.rb

@@ -820,8 +820,8 @@ module Enumerable
     return to_enum(:filter_map) unless blk
 
     ary = []
-    self.each do |x|
-      x = blk.call(x)
+    self.each do |*x|
+      x = blk.call(*x)
       ary.push x if x
     end
     ary