to_hash/to_a check in Hash[] should only be done when only one argument is given; ref #2594

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

@@ -24,6 +24,8 @@ class Hash
   #
 
   def self.[](*object)
+    length = object.length
+    if length == 1
       o = object[0]
       if o.respond_to?(:to_hash)
         h = Hash.new
@@ -47,9 +49,12 @@ class Hash
         end
         return h
       end
-    raise ArgumentError, 'odd number of arguments for Hash' unless object.length % 2 == 0
+    end
+    unless length % 2 == 0
+      raise ArgumentError, 'odd number of arguments for Hash'
+    end
     h = Hash.new
-    0.step(object.length - 2, 2) do |i|
+    0.step(length - 2, 2) do |i|
       h[object[i]] = object[i + 1]
     end
     h