fix SetMesh warning

ImGuiNET.Unity/Renderer/ImGuiRendererMesh.cs

@@ -3,6 +3,7 @@
 using Unity.Collections;
 using Unity.Collections.LowLevel.Unsafe;
 using Unity.Profiling;
+using System.Collections.Generic;
 
 namespace ImGuiNET.Unity
 {
@@ -32,7 +33,7 @@ sealed class ImGuiRendererMesh : IImGuiRenderer
         const MeshUpdateFlags NoMeshChecks = MeshUpdateFlags.DontNotifyMeshUsers | MeshUpdateFlags.DontRecalculateBounds
                                            | MeshUpdateFlags.DontResetBoneBounds | MeshUpdateFlags.DontValidateIndices;
         int _prevSubMeshCount = 1;  // number of sub meshes used previously
-
+        List<SubMeshDescriptor> descriptors = new List<SubMeshDescriptor>();
         static readonly ProfilerMarker s_updateMeshPerfMarker = new ProfilerMarker("DearImGui.RendererMesh.UpdateMesh");
         static readonly ProfilerMarker s_createDrawComandsPerfMarker = new ProfilerMarker("DearImGui.RendererMesh.CreateDrawCommands");
 
@@ -96,7 +97,7 @@ unsafe void UpdateMesh(ImDrawDataPtr drawData, Vector2 fbSize)
             // upload data into mesh
             int vtxOf = 0;
             int idxOf = 0;
-            int subOf = 0;
+
             for (int n = 0, nMax = drawData.CmdListsCount; n < nMax; ++n)
             {
                 ImDrawListPtr drawList = drawData.CmdListsRange[n];
@@ -112,7 +113,7 @@ unsafe void UpdateMesh(ImDrawDataPtr drawData, Vector2 fbSize)
                 // upload vertex/index data
                 _mesh.SetVertexBufferData(vtxArray, 0, vtxOf, vtxArray.Length, 0, NoMeshChecks);
                 _mesh.SetIndexBufferData (idxArray, 0, idxOf, idxArray.Length,    NoMeshChecks);
-
+                descriptors.Clear();
                 // define subMeshes
                 for (int i = 0, iMax = drawList.CmdBuffer.Size; i < iMax; ++i)
                 {
@@ -124,11 +125,12 @@ unsafe void UpdateMesh(ImDrawDataPtr drawData, Vector2 fbSize)
                         indexCount = (int)cmd.ElemCount,
                         baseVertex = vtxOf + (int)cmd.VtxOffset,
                     };
-                    _mesh.SetSubMesh(subOf++, descriptor, NoMeshChecks);
+                    descriptors.Add(descriptor);
                 }
                 vtxOf += vtxArray.Length;
                 idxOf += idxArray.Length;
             }
+            _mesh.SetSubMeshes(descriptors, NoMeshChecks);
             _mesh.UploadMeshData(false);
         }