Check Content\Item::replaceTag return for false return value before using it

- Address https://github.com/friendica/friendica/issues/10169#issuecomment-835547443
- Remove unused code in Content\Item::replaceTag

mod/item.php

@@ -410,7 +410,7 @@ function item_post(App $a) {
 				}
 			}
 
-			$success = ItemHelper::replaceTag($body, $inform, local_user() ? local_user() : $profile_uid, $tag, $network);
+			if ($success = ItemHelper::replaceTag($body, $inform, local_user() ? local_user() : $profile_uid, $tag, $network)) {
 				if ($success['replaced']) {
 					$tagged[] = $tag;
 				}
@@ -427,6 +427,7 @@ function item_post(App $a) {
 					$forum_contact = $success['contact'];
 				}
 			}
+		}
 
 		return $body;
 	});

src/Content/Item.php

@@ -127,16 +127,6 @@ class Item
 			$tag_type = substr($tag, 0, 1);
 			//is it already replaced?
 			if (strpos($tag, '[url=')) {
-				// Checking for the alias that is used for OStatus
-				$pattern = '/[@!]\[url\=(.*?)\](.*?)\[\/url\]/ism';
-				if (preg_match($pattern, $tag, $matches)) {
-					$data = Contact::getByURL($matches[1], false, ['alias', 'nick']);
-
-					if ($data['alias'] != '') {
-						$newtag = '@[url=' . $data['alias'] . ']' . $data['nick'] . '[/url]';
-					}
-				}
-
 				return $replaced;
 			}
 

src/Content/Text/BBCode.php

@@ -2196,9 +2196,7 @@ class BBCode
 					}
 				}
 
-				$success = Item::replaceTag($body, $inform, $profile_uid, $tag, $network);
+				if (($success = Item::replaceTag($body, $inform, $profile_uid, $tag, $network)) && $success['replaced']) {
-
-				if ($success['replaced']) {
 					$tagged[] = $tag;
 				}
 			}