Fix error displaying scout messages

In the `displayGrouped` and `displayMessage` functions, we now return
the constructed message (an array) instead of passing in the message
box by reference and appending to it inside the functions.

This fixes an issue with scout messages where the "GroupedMessages"
element did not yet exist, but we were passing it by reference to the
`displayMessage` function as if it were an array. This caused the
following error:

> TypeError: displayMessage(): Argument #1 ($messageBox) must be of type array, null given

src/engine/Default/message_view.php

@@ -87,7 +87,7 @@
 	$template->unassign('NextPageHREF'); // always displaying all scout messages?
 } else {
 	foreach ($dbResult->records() as $dbRecord) {
-		displayMessage($messageBox, $dbRecord->getInt('message_id'), $dbRecord->getInt('account_id'), $dbRecord->getInt('sender_id'), $player->getGameID(), $dbRecord->getString('message_text'), $dbRecord->getInt('send_time'), $dbRecord->getBoolean('msg_read'), $var['folder_id'], $player->getAccount());
+		$messageBox['Messages'][] = displayMessage($dbRecord->getInt('message_id'), $dbRecord->getInt('account_id'), $dbRecord->getInt('sender_id'), $player->getGameID(), $dbRecord->getString('message_text'), $dbRecord->getInt('send_time'), $dbRecord->getBoolean('msg_read'), $var['folder_id'], $player->getAccount());
 	}
 }
 if (!USING_AJAX) {
@@ -115,7 +115,7 @@ function displayScouts(array &$messageBox, SmrPlayer $player) : void {
 		$totalUnread = $dbRecord->getInt('total_unread');
 		$message = 'Your forces have spotted ' . $sender->getBBLink() . ' passing your forces ' . $dbRecord->getInt('number') . ' ' . pluralise('time', $dbRecord->getInt('number'));
 		$message .= ($totalUnread > 0) ? ' (' . $totalUnread . ' unread).' : '.';
-		displayGrouped($messageBox, $sender, $message, $dbRecord->getInt('first'), $dbRecord->getInt('last'), $totalUnread > 0, $player->getAccount());
+		$messageBox['Messages'][] = displayGrouped($sender, $message, $dbRecord->getInt('first'), $dbRecord->getInt('last'), $totalUnread > 0, $player->getAccount());
 	}
 
 	// Now display individual messages in each group
@@ -131,15 +131,15 @@ function displayScouts(array &$messageBox, SmrPlayer $player) : void {
 		$groupBox =& $messageBox['GroupedMessages'][$dbRecord->getInt('sender_id')];
 		// Limit the number of messages in each group
 		if (!isset($groupBox['Messages']) || count($groupBox['Messages']) < MESSAGE_SCOUT_GROUP_LIMIT) {
-			displayMessage($groupBox, $dbRecord->getInt('message_id'), $dbRecord->getInt('account_id'), $dbRecord->getInt('sender_id'), $player->getGameID(), $dbRecord->getString('message_text'), $dbRecord->getInt('send_time'), $dbRecord->getBoolean('msg_read'), MSG_SCOUT, $player->getAccount());
+			$groupBox['Messages'][] = displayMessage($dbRecord->getInt('message_id'), $dbRecord->getInt('account_id'), $dbRecord->getInt('sender_id'), $player->getGameID(), $dbRecord->getString('message_text'), $dbRecord->getInt('send_time'), $dbRecord->getBoolean('msg_read'), MSG_SCOUT, $player->getAccount());
 		}
 	}
 
 	// In the default view (groups), we're always displaying all messages
 	$messageBox['NumberMessages'] = $dbResult->getNumRecords();
 }
 
-function displayGrouped(array &$messageBox, SmrPlayer $sender, string $message_text, int $first, int $last, bool $star, SmrAccount $displayAccount) : void {
+function displayGrouped(SmrPlayer $sender, string $message_text, int $first, int $last, bool $star, SmrAccount $displayAccount) : array {
 	// Define a unique array so we can delete grouped messages
 	$array = array(
 		$sender->getAccountID(),
@@ -154,10 +154,10 @@ function displayGrouped(array &$messageBox, SmrPlayer $sender, string $message_t
 	$message['SenderDisplayName'] = $sender->getLinkedDisplayName(false);
 	$message['SendTime'] = date($displayAccount->getDateTimeFormat(), $first) . " - " . date($displayAccount->getDateTimeFormat(), $last);
 	$message['Text'] = $message_text;
-	$messageBox['Messages'][] = $message;
+	return $message;
 }
 
-function displayMessage(array &$messageBox, int $message_id, int $receiver_id, int $sender_id, int $game_id, string $message_text, int $send_time, bool $msg_read, int $type, SmrAccount $displayAccount) : void {
+function displayMessage(int $message_id, int $receiver_id, int $sender_id, int $game_id, string $message_text, int $send_time, bool $msg_read, int $type, SmrAccount $displayAccount) : array {
 	$message = array();
 	$message['ID'] = $message_id;
 	$message['Text'] = $message_text;
@@ -201,6 +201,5 @@ function displayMessage(array &$messageBox, int $message_id, int $receiver_id, i
 		$message['ReceiverDisplayName'] = create_link($container, $receiver->getDisplayName());
 	}
 
-	// Append the message to this box
-	$messageBox['Messages'][] = $message;
+	return $message;
 }