[Vulkan] Don't skip drawing when there's no vertexes to ensure that u…

…ser callbacks are still processed.

examples/imgui_impl_vulkan.cpp

@@ -278,6 +278,7 @@ static void ImGui_ImplVulkan_SetupRenderState(ImDrawData* draw_data, VkCommandBu
     }
 
     // Bind Vertex And Index Buffer:
+    if (draw_data->TotalVtxCount > 0)
     {
         VkBuffer vertex_buffers[1] = { rb->VertexBuffer };
         VkDeviceSize vertex_offset[1] = { 0 };
@@ -320,7 +321,7 @@ void ImGui_ImplVulkan_RenderDrawData(ImDrawData* draw_data, VkCommandBuffer comm
     // Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
     int fb_width = (int)(draw_data->DisplaySize.x * draw_data->FramebufferScale.x);
     int fb_height = (int)(draw_data->DisplaySize.y * draw_data->FramebufferScale.y);
-    if (fb_width <= 0 || fb_height <= 0 || draw_data->TotalVtxCount == 0)
+    if (fb_width <= 0 || fb_height <= 0)
         return;
 
     ImGuiIO& io = ImGui::GetIO();
@@ -344,12 +345,14 @@ void ImGui_ImplVulkan_RenderDrawData(ImDrawData* draw_data, VkCommandBuffer comm
     // Create or resize the vertex/index buffers
     size_t vertex_size = draw_data->TotalVtxCount * sizeof(ImDrawVert);
     size_t index_size = draw_data->TotalIdxCount * sizeof(ImDrawIdx);
+
     if (rb->VertexBuffer == VK_NULL_HANDLE || rb->VertexBufferSize < vertex_size)
         CreateOrResizeBuffer(rb->VertexBuffer, rb->VertexBufferMemory, rb->VertexBufferSize, vertex_size, VK_BUFFER_USAGE_VERTEX_BUFFER_BIT);
     if (rb->IndexBuffer == VK_NULL_HANDLE || rb->IndexBufferSize < index_size)
         CreateOrResizeBuffer(rb->IndexBuffer, rb->IndexBufferMemory, rb->IndexBufferSize, index_size, VK_BUFFER_USAGE_INDEX_BUFFER_BIT);
 
     // Upload vertex/index data into a single contiguous GPU buffer
+    if (vertex_size)
     {
         ImDrawVert* vtx_dst = NULL;
         ImDrawIdx* idx_dst = NULL;