Fix let-env (#3057)

crates/nu-command/src/script.rs

@@ -184,7 +184,7 @@ pub async fn process_script(
         trace!("{:#?}", block);
         let env = ctx.get_env();
 
-        ctx.scope.add_env(env);
+        ctx.scope.add_env_to_base(env);
         let result = run_block(&block, ctx, input_stream).await;
         match result {
             Ok(input) => {

crates/nu-engine/src/evaluate/scope.rs

@@ -186,6 +186,12 @@ impl Scope {
             frame.env.extend(env_vars)
         }
     }
+
+    pub fn add_env_to_base(&self, env_vars: IndexMap<String, String>) {
+        if let Some(frame) = self.frames.lock().first_mut() {
+            frame.env.extend(env_vars)
+        }
+    }
 }
 
 impl ParserScope for Scope {