runtime: Fix runtime/cdi panic with assignment to entry in nil map

It will panic when users do GPU vfio passthrough with cdi in runtime.
The root cause is that CustomSpec.Annotations is nil when new element
added.
To address this issue, initialization is introduced when it's nil.

Fixes #10266

Signed-off-by: Alex Lyn <alex.lyn@antgroup.com>

src/runtime/virtcontainers/container.go

@@ -1010,6 +1010,9 @@ func (c *Container) siblingAnnotation(devPath string, siblings []DeviceRelation)
 			vfioNum := filepath.Base(devPath)
 			annoKey := fmt.Sprintf("cdi.k8s.io/vfio%s", vfioNum)
 			annoValue := fmt.Sprintf("nvidia.com/gpu=%d", sibling.Index)
+			if c.config.CustomSpec.Annotations == nil {
+				c.config.CustomSpec.Annotations = make(map[string]string)
+			}
 			c.config.CustomSpec.Annotations[annoKey] = annoValue
 			c.Logger().Infof("annotated container with %s: %s", annoKey, annoValue)
 		}