manifest: Fix crash on startup when trying to clean up unused files (#5840)

Currently if the config field is missing in the manifest file (or
corrupted), Ollama will crash when it tries to read it. This can
happen at startup or when pulling new models.

This data is mostly just used for showing model information so we
can be tolerant of it not being present - it is not required to
run the models. Besides avoiding crashing, this also gives us the
ability to restructure the config in the future by pulling it
into the main manifest file.

server/manifest.go

@@ -16,7 +16,7 @@ import (
 type Manifest struct {
 	SchemaVersion int      `json:"schemaVersion"`
 	MediaType     string   `json:"mediaType"`
-	Config        *Layer   `json:"config"`
+	Config        Layer    `json:"config"`
 	Layers        []*Layer `json:"layers"`
 
 	filepath string
@@ -25,7 +25,7 @@ type Manifest struct {
 }
 
 func (m *Manifest) Size() (size int64) {
-	for _, layer := range append(m.Layers, m.Config) {
+	for _, layer := range append(m.Layers, &m.Config) {
 		size += layer.Size
 	}
 
@@ -46,11 +46,13 @@ func (m *Manifest) Remove() error {
 }
 
 func (m *Manifest) RemoveLayers() error {
-	for _, layer := range append(m.Layers, m.Config) {
-		if err := layer.Remove(); errors.Is(err, os.ErrNotExist) {
-			slog.Debug("layer does not exist", "digest", layer.Digest)
-		} else if err != nil {
-			return err
+	for _, layer := range append(m.Layers, &m.Config) {
+		if layer.Digest != "" {
+			if err := layer.Remove(); errors.Is(err, os.ErrNotExist) {
+				slog.Debug("layer does not exist", "digest", layer.Digest)
+			} else if err != nil {
+				return err
+			}
 		}
 	}
 
@@ -113,7 +115,7 @@ func WriteManifest(name model.Name, config *Layer, layers []*Layer) error {
 	m := Manifest{
 		SchemaVersion: 2,
 		MediaType:     "application/vnd.docker.distribution.manifest.v2+json",
-		Config:        config,
+		Config:        *config,
 		Layers:        layers,
 	}