GPU: Add assert on zero sized VBOs

These can create GL errors that are not reported
appropriately.

source/blender/draw/intern/draw_instance_data.cc

@@ -215,7 +215,6 @@ void DRW_instance_buffer_finish(DRWInstanceDataList *idatalist)
         GPU_vertbuf_data_resize(*handle->buf, target_buf_size);
       }
       GPU_vertbuf_data_len_set(*handle->buf, vert_len);
-      GPU_vertbuf_use(handle->buf); /* Send data. */
     }
   }
   /* Finish pending instancing batches. */

source/blender/gpu/opengl/gl_vertex_buffer.cc

@@ -93,6 +93,8 @@ void GLVertBuf::bind()
 
   if (flag & GPU_VERTBUF_DATA_DIRTY) {
     vbo_size_ = this->size_used_get();
+
+    BLI_assert(vbo_size_ != 0);
     /* Orphan the vbo to avoid sync then upload data. */
     glBufferData(GL_ARRAY_BUFFER, ceil_to_multiple_ul(vbo_size_, 16), nullptr, to_gl(usage_));
     /* Do not transfer data from host to device when buffer is device only. */