if in doubt, prefer unwrap_or_default()

if the past we had lots of crashes because of unexpected unwrap failures,
mostly related to string.
this commit avoids them eg. for string-conversions that may panic
eg. when encountering a null-byte or by logical programming errors
where an object is assumed to be set but is not under unexpected circumstances.

src/context.rs

@@ -330,7 +330,7 @@ impl Context {
                     Ok(ret)
                 },
             )
-            .unwrap()
+            .unwrap_or_default()
     }
 
     #[allow(non_snake_case)]