Don't print 'Ignoring cache image "cache-image-name" because it was c…

…orrupt' (buildpacks#1185)

when the cache image is not found

Signed-off-by: Natalie Arellano <narellano@vmware.com>

cache/image_cache.go

@@ -77,7 +77,7 @@ func (c *ImageCache) SetMetadata(metadata platform.CacheMetadata) error {
 }
 
 func (c *ImageCache) RetrieveMetadata() (platform.CacheMetadata, error) {
-	if !c.origImage.Valid() {
+	if c.origImage.Found() && !c.origImage.Valid() {
 		c.logger.Infof("Ignoring cache image %q because it was corrupt", c.origImage.Name())
 		return platform.CacheMetadata{}, nil
 	}