Fix handling of empty array optional argument rb prototype

The rubyvm code only handled `LIST` but should have checked `ZLIST` as well.
As such the type was untyped previously

Author: Earlopain

lib/rbs/prototype/rb.rb

@@ -838,12 +838,7 @@ def param_type(node, default: Types::Bases::Any.new(location: nil))
           when Prism::TrueNode, Prism::FalseNode
             Types::Bases::Bool.new(location: nil)
           when Prism::ArrayNode
-            # FIXME bug replicating empty array untyped
-            if node.elements.any?
-              BuiltinNames::Array.instance_type(default)
-            else
-              default
-            end
+            BuiltinNames::Array.instance_type(default)
           when Prism::HashNode
             BuiltinNames::Hash.instance_type(default, default)
           else

test/rbs/rb_prototype_test.rb

@@ -49,6 +49,8 @@ def self.world
   end
 
   def kw_req(a:) end
+
+  def empty_array_opt(a = []) end
 end
     EOR
 
@@ -59,6 +61,8 @@ def hello: (untyped a, ?::Integer b, *untyped c, untyped d, e: untyped, ?f: ::In
   def self.world: () { (untyped, untyped, untyped, x: untyped, y: untyped) -> untyped } -> untyped
 
   def kw_req: (a: untyped) -> nil
+
+  def empty_array_opt: (?::Array[untyped] a) -> nil
 end
     EOF
   end