Fix: Crash when using Vulkan backend.

Command buffer was not availble at the time dummy buffers are
initialized. Resulting in undefined behavior.

source/blender/gpu/vulkan/vk_backend.cc

@@ -135,7 +135,6 @@ Context *VKBackend::context_alloc(void *ghost_window, void *ghost_context)
 
   VKContext *context = new VKContext(ghost_window, ghost_context);
   device_.context_register(*context);
-  device_.init_dummy_buffer(*context);
   return context;
 }
 

source/blender/gpu/vulkan/vk_context.cc

@@ -78,6 +78,7 @@ void VKContext::sync_backbuffer()
     command_buffer_.init(device.device_get(), device.queue_get(), command_buffer);
     command_buffer_.begin_recording();
     device.descriptor_pools_get().reset();
+    device.init_dummy_buffer(*this);
   }
 }
 

source/blender/gpu/vulkan/vk_device.hh

@@ -127,6 +127,12 @@ class VKDevice : public NonCopyable {
 
   bool is_initialized() const;
   void init(void *ghost_context);
+  /**
+   * Initialize a dummy buffer that can be bound for missing attributes.
+   *
+   * Dummy buffer can only be initialized after the command buffer of the context is retrieved.
+   */
+  void init_dummy_buffer(VKContext &context);
   void deinit();
 
   eGPUDeviceType device_type() const;
@@ -159,7 +165,6 @@ class VKDevice : public NonCopyable {
   void init_debug_callbacks();
   void init_memory_allocator();
   void init_descriptor_pools();
-  void init_dummy_buffer(VKContext &context);
 
   /* During initialization the backend requires access to update the workarounds. */
   friend VKBackend;