Merge pull request #55 from jfontan/fix/copypath

Some errors are lost in copyPath
diff --git a/helper/mount/mount.go b/helper/mount/mount.go
index 847d196..bb13da5 100644
--- a/helper/mount/mount.go
+++ b/helper/mount/mount.go
@@ -228,12 +228,12 @@
 
 	srcFile, err := src.Open(srcPath)
 	if err != nil {
-		return nil
+		return err
 	}
 
 	_, err = io.Copy(dstFile, srcFile)
 	if err != nil {
-		return nil
+		return err
 	}
 
 	err = dstFile.Close()