check if array expands in each block

mrblib/array.rb

@@ -11,7 +11,7 @@ class Array
   # ISO 15.2.12.5.10
   def each(&block)
     idx, length = -1, self.length-1
-    while(idx < length)
+    while idx < length and length < self.length and length = self.length-1
       elm = self[idx += 1]
       unless elm
         if elm == nil and length >= self.length