fix: check for user account status before attemping to process email change.

changelog.d/2298.bugfix

@@ -0,0 +1 @@
+"!admin users change-email" now verifies a user exists before attempting to change their email. Contributed by @Clubs.

src/admin/user/commands.rs

@@ -1083,6 +1083,9 @@ pub(super) async fn get_user_by_email(&self, email: String) -> Result {
 
 	pub(super) async fn change_email(&self, user_id: String, email: Option<String>) -> Result {
 		let user_id = parse_local_user_id(self.services, &user_id)?;
+		if matches!(self.services.users.status(&user_id).await, AccountStatus::NotFound) {
+			return Err!("This account does not exist.");
+		}
 		let Ok(new_email) = email.map(Address::try_from).transpose() else {
 			return Err!("Invalid email address.");
 		};