Do not transform (parse) commands that fail inside of a pipeline, like

`#zrange` with invalid parameters and `with_scores` set to `true`. This
last argument requires parsing of the result, but when the Redis server
returns a `CommandError`, this string is attempted to be parsed, which
fails with the following stacktrace:

```
/Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis.rb:2809:in
`block in <class:Redis>': undefined method `each_slice' for
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/pipeline.rb:114:in
  `_set'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/pipeline.rb:61:in
  `block in finish'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/pipeline.rb:60:in
  `each'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/pipeline.rb:60:in
  `each_with_index'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/pipeline.rb:60:in
  `each'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/pipeline.rb:60:in
  `map'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/pipeline.rb:60:in
  `finish'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/client.rb:155:in
  `block in call_pipeline'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/client.rb:291:in
  `with_reconnect'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis/client.rb:153:in
  `call_pipeline'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis.rb:2307:in
  `block in pipelined'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis.rb:45:in
  `block in synchronize'
  from
  /Users/javierhonduco/.rubies/ruby-2.4.0/lib/ruby/2.4.0/monitor.rb:214:in
  `mon_synchronize'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis.rb:45:in
  `synchronize'
  from
  /Users/javierhonduco/.gem/ruby/2.4.0/gems/redis-4.0.1/lib/redis.rb:2303:in
  `pipelined'
  [...]
```

Author: javierhonduco

lib/redis.rb

@@ -2805,11 +2805,13 @@ def method_missing(command, *args)
     }
 
   FloatifyPairs =
-    lambda { |array|
-      if array
-        array.each_slice(2).map do |member, score|
+    lambda { |result|
+      if result.respond_to?(:each_slice)
+        result.each_slice(2).map do |member, score|
           [member, Floatify.call(score)]
         end
+      else
+        result
       end
     }
 

test/pipelining_commands_test.rb

@@ -128,6 +128,14 @@ def test_futures_raise_when_trying_to_access_their_values_too_early
     end
   end
 
+  def test_futures_raise_when_command_errors_and_needs_transformation
+    assert_raise(Redis::CommandError) do
+      r.pipelined do
+        @result = r.zrange("a", "b", 5, :with_scores => true)
+      end
+    end
+  end
+
   def test_futures_can_be_identified
     r.pipelined do
       @result = r.sadd("foo", 1)