Fix non-zero exit code errors in middle of pipeline (#13899)

# Description
Fixes #13868. Should come after #13885.

# User-Facing Changes
Bug fix.

# Tests + Formatting
Added a test.

crates/nu-command/src/filesystem/save.rs

@@ -182,6 +182,8 @@ impl Command for Save {
                             }
                             (None, None) => {}
                         };
+
+                        child.wait()?;
                     }
                 }