ocicrypt-rs: dont't swallop pre_unwrap_key() error

The error for encryption::pre_unwrap_key() is silently discarded, which
means we get no meaningful error in consumers.

Signed-off-by: Magnus Kulke <magnuskulke@microsoft.com>

ocicrypt-rs/src/encryption.rs

@@ -188,10 +188,9 @@ pub fn decrypt_layer_key_opts_data(
                 priv_key_given = true;
             }
 
-            if let Ok(opts_data) = pre_unwrap_key(keywrapper, dc, &b64_annotation) {
-                if !opts_data.is_empty() {
-                    return Ok(opts_data);
-                }
+            let opts_data = pre_unwrap_key(keywrapper, dc, &b64_annotation)?;
+            if !opts_data.is_empty() {
+                return Ok(opts_data);
             }
             // try next keywrapper
         }