libcontainer/specconv/spec_linux: Avoid panic when Process is unset

As it can be since opencontainers/runtime-spec@c41ea83d (config: Make
process optional, 2017-02-27, opencontainers/runtime-spec#701).

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

libcontainer/specconv/spec_linux.go

@@ -238,19 +238,21 @@ func CreateLibcontainerConfig(opts *CreateOpts) (*configs.Config, error) {
 			config.Seccomp = seccomp
 		}
 	}
-	if spec.Process.SelinuxLabel != "" {
-		config.ProcessLabel = spec.Process.SelinuxLabel
-	}
-	if spec.Process != nil && spec.Process.OOMScoreAdj != nil {
-		config.OomScoreAdj = *spec.Process.OOMScoreAdj
-	}
-	if spec.Process.Capabilities != nil {
-		config.Capabilities = &configs.Capabilities{
-			Bounding:    spec.Process.Capabilities.Bounding,
-			Effective:   spec.Process.Capabilities.Effective,
-			Permitted:   spec.Process.Capabilities.Permitted,
-			Inheritable: spec.Process.Capabilities.Inheritable,
-			Ambient:     spec.Process.Capabilities.Ambient,
+	if spec.Process != nil {
+		if spec.Process.SelinuxLabel != "" {
+			config.ProcessLabel = spec.Process.SelinuxLabel
+		}
+		if spec.Process.OOMScoreAdj != nil {
+			config.OomScoreAdj = *spec.Process.OOMScoreAdj
+		}
+		if spec.Process.Capabilities != nil {
+			config.Capabilities = &configs.Capabilities{
+				Bounding:    spec.Process.Capabilities.Bounding,
+				Effective:   spec.Process.Capabilities.Effective,
+				Permitted:   spec.Process.Capabilities.Permitted,
+				Inheritable: spec.Process.Capabilities.Inheritable,
+				Ambient:     spec.Process.Capabilities.Ambient,
+			}
 		}
 	}
 	createHooks(spec, config)