Backends: Vulkan: ImGui_ImplVulkan_AddTexture() skips updating descriptor_set if failing to allocate. (#8677)

Reduce error surface to the check_vk_result() call.

backends/imgui_impl_vulkan.cpp

@@ -1376,6 +1376,7 @@ VkDescriptorSet ImGui_ImplVulkan_AddTexture(VkSampler sampler, VkImageView image
     }
 
     // Update the Descriptor Set:
+    if (descriptor_set != VK_NULL_HANDLE)
     {
         VkDescriptorImageInfo desc_image[1] = {};
         desc_image[0].sampler = sampler;