fix: Warn when sending empty gumps (#2563)

### Summary

Generates a console warning when users receive an empty gump. This will help prevent client side leaks.

Projects/UOContent.Tests/Tests/Gumps/TestGumps/DynamicTestGump.cs

@@ -6,6 +6,8 @@ public class DynamicTestGump : DynamicGump
 {
     private readonly string _petName;
 
+    public bool HasVisualElementsForTest => HasVisualElements;
+
     public DynamicTestGump(string petName) : base(50, 50)
     {
         _petName = petName;

Projects/UOContent.Tests/Tests/Gumps/TestGumps/EmptyTestGumps.cs

@@ -0,0 +1,40 @@
+using Server.Gumps;
+
+namespace Server.Tests.Gumps;
+
+public sealed class EmptyLegacyTestGump : Gump
+{
+    public bool HasVisualElementsForTest => HasVisualElements;
+
+    public EmptyLegacyTestGump() : base(0, 0)
+    {
+    }
+}
+
+public sealed class EmptyDynamicTestGump : DynamicGump
+{
+    public bool HasVisualElementsForTest => HasVisualElements;
+
+    public EmptyDynamicTestGump() : base(0, 0)
+    {
+    }
+
+    protected override void BuildLayout(ref DynamicGumpBuilder builder)
+    {
+        builder.AddPage();
+    }
+}
+
+public sealed class EmptyStaticTestGump : StaticGump<EmptyStaticTestGump>
+{
+    public bool HasVisualElementsForTest => HasVisualElements;
+
+    public EmptyStaticTestGump() : base(0, 0)
+    {
+    }
+
+    protected override void BuildLayout(ref StaticGumpBuilder builder)
+    {
+        builder.SetNoClose();
+    }
+}

Projects/UOContent.Tests/Tests/Gumps/TestGumps/LegacyTestGump.cs

@@ -4,6 +4,8 @@ namespace Server.Tests.Gumps;
 
 public sealed class LegacyTestGump : Gump
 {
+    public bool HasVisualElementsForTest => HasVisualElements;
+
     public LegacyTestGump(string petName) : base(50, 50)
     {
         Serial = (Serial)0x123;

Projects/UOContent.Tests/Tests/Gumps/TestGumps/StaticTestGump.cs

@@ -4,6 +4,8 @@ namespace Server.Tests.Gumps;
 
 public class StaticTestGump : StaticGump<StaticTestGump>
 {
+    public bool HasVisualElementsForTest => HasVisualElements;
+
     public StaticTestGump() : base(50, 50)
     {
         Serial = (Serial)0x123;

Projects/UOContent.Tests/Tests/Gumps/TestLayoutGumps.cs

@@ -73,6 +73,32 @@ public class TestLayoutGumps
         AssertThat.Equal(writer.Span, packet);
     }
 
+    [Fact]
+    public void TestEmptyGumpsHaveNoVisualElements()
+    {
+        Assert.False(Compile(new EmptyLegacyTestGump()).HasVisualElementsForTest);
+        Assert.False(Compile(new EmptyDynamicTestGump()).HasVisualElementsForTest);
+        Assert.False(Compile(new EmptyStaticTestGump()).HasVisualElementsForTest);
+        Assert.False(Compile(new EmptyStaticTestGump()).HasVisualElementsForTest);
+    }
+
+    [Fact]
+    public void TestVisibleGumpsHaveVisualElements()
+    {
+        Assert.True(Compile(new LegacyTestGump("Test")).HasVisualElementsForTest);
+        Assert.True(Compile(new DynamicTestGump("Test")).HasVisualElementsForTest);
+        Assert.True(Compile(new StaticTestGump()).HasVisualElementsForTest);
+        Assert.True(Compile(new StaticTestGump()).HasVisualElementsForTest);
+    }
+
+    private static T Compile<T>(T gump) where T : BaseGump
+    {
+        var buffer = GC.AllocateUninitializedArray<byte>(512);
+        var writer = new SpanWriter(buffer);
+        gump.Compile(ref writer);
+        return gump;
+    }
+
     private static void InternalTestStaticGump<T>(ReadOnlySpan<byte> expectedLayout, StaticGump<T> staticGump, string[] strings)
         where T : StaticGump<T>
     {