rust: add macro to return val if unwrap fails

rust/src/debug.rs

@@ -236,3 +236,13 @@ macro_rules! debug_validate_fail (
     }
   };
 );
+
+#[macro_export]
+macro_rules! unwrap_or_return (
+    ($e:expr, $r:expr) => {
+        match $e {
+            Ok(x) => x,
+            Err(_) => return $r,
+        }
+    };
+);