Fix ErrorImpl::source to return Some for inner error

Correct the logic to preserve each source level: avoid direct source
recursion and unwrap the inner error instead.

Signed-off-by: Nicola Bonelli <nicola.bonelli@huawei-partners.com>

Author: awgn

orion-error/src/lib.rs

@@ -278,8 +278,7 @@ enum ErrorImpl {
 impl ErrorTrait for ErrorImpl {
     fn source(&self) -> Option<&(dyn ErrorTrait + 'static)> {
         match self {
-            Self::Error(err) => err.source(),
-            Self::Context(_, err) => err.source(),
+            Self::Error(err) | Self::Context(_, err) => Some(err.as_ref()),
         }
     }
 }