Fix returning [Type, false] from resolve_type

[swalkinshaw]

#4130 fixed returning [Type, nil] from a union's resolve_type, but it caused a regression for literal false values.

Schema#resolve_type had an if resolved_value conditional would be false for false values causing it always return a single value (the resolve_type).

The runtime's resolve_type method would then always return the tuple version (in non-lazy cases): [type, value]. However, since Schema#resolve_type was only returning a single value, the resolved value would be lost resulting in [type, nil] being passed on.

The fix is to remove the if resolved_value conditional entirely and always return the two-value tuple ensuring the original resolved value is correctly passed along.

Note: the runtime still has a branch to check if the resolve_type value is a tuple or not. The only case where this won't be true is for lazy resolved types.

The call stack is a bit confusing, so here's all the relevant code in call order:

1. Schema#resolve_type
   

   graphql-ruby/lib/graphql/schema.rb

   Lines 802 to 806 in 42b3413

   	if resolved_value
   	[resolved_type, resolved_value]
   	else
   	resolved_type
   	end

2. Runtime#resolve_type
   

   graphql-ruby/lib/graphql/execution/interpreter/runtime.rb

   Line 992 in 42b3413

   [resolved_type, resolved_value]

3. Runtime#continue_field
   

   graphql-ruby/lib/graphql/execution/interpreter/runtime.rb

   Lines 725 to 730 in 42b3413

   	if resolved_type_result.is_a?(Array) && resolved_type_result.length == 2
   	resolved_type, resolved_value = resolved_type_result
   	else
   	resolved_type = resolved_type_result
   	resolved_value = value
   	end

cc @IDolgirev

[rmosolgo]

Wow -- thanks for the fix and test on this!

[swalkinshaw]

Thanks for the backport!