Hide splat label in certain situations

Undefined double methods were reporting splat arguments, which is technically correct.
But for output in these cases, it makes more sense to show the exact calling args.

spec/spectator/mocks/arguments_spec.cr

@@ -97,6 +97,14 @@ Spectator.describe Spectator::Arguments do
         is_expected.to eq("(no args)")
       end
     end
+
+    context "with a splat and no arguments" do
+      let(arguments) { Spectator::Arguments.build(NamedTuple.new, :splat, {:x, :y, :z}, {bar: "baz", qux: 123}) }
+
+      it "omits the splat name" do
+        is_expected.to eq("(:x, :y, :z, bar: \"baz\", qux: 123)")
+      end
+    end
   end
 
   describe "#==" do

src/spectator/mocks/arguments.cr

@@ -107,14 +107,14 @@ module Spectator
       # Add the splat arguments.
       if (splat = @splat) && !splat.empty?
         io << ", " unless args.empty?
-        if name = @splat_name
-          io << '*' << name << ": {"
+        if splat_name = !args.empty? && @splat_name
+          io << '*' << splat_name << ": {"
         end
         splat.each_with_index do |arg, i|
           io << ", " if i > 0
           arg.inspect(io)
         end
-        io << '}' if @splat_name
+        io << '}' if splat_name
       end
 
       # Add the keyword arguments.