Fixes bug where the schema copy constructor would run into a stack overflow due to wrong copying of AdditionalProperties object

Author: MaggieKimani1

src/Microsoft.OpenApi/Models/OpenApiSchema.cs

@@ -280,7 +280,7 @@ public OpenApiSchema(OpenApiSchema schema)
             MaxProperties = schema?.MaxProperties ?? MaxProperties;
             MinProperties = schema?.MinProperties ?? MinProperties;
             AdditionalPropertiesAllowed = schema?.AdditionalPropertiesAllowed ?? AdditionalPropertiesAllowed;
-            AdditionalProperties = new(schema?.AdditionalProperties);
+            AdditionalProperties = schema?.AdditionalProperties != null ? new(schema?.AdditionalProperties) : null;
             Discriminator = schema?.Discriminator != null ? new(schema?.Discriminator) : null;
             Example = OpenApiAnyCloneHelper.CloneFromCopyConstructor(schema?.Example);
             Enum = schema?.Enum != null ? new List<IOpenApiAny>(schema.Enum) : null;