Remove Option from source and use empty string as no source.

src/api/eval.rs

@@ -209,9 +209,8 @@ impl Engine {
         level: usize,
     ) -> RhaiResult {
         let mut state = EvalState::new();
-        if ast.source_raw().is_some() {
-            global.source = ast.source_raw().cloned();
-        }
+        global.source = ast.source_raw().clone();
+
         #[cfg(not(feature = "no_module"))]
         {
             global.embedded_module_resolver = ast.resolver().cloned();