Fix potential bugs without expected behavior change

- Fix uninitialized variables
- Fix potentially not set variables
- Fix wrong parameter default value
- Fix method scope
- Fix missing return value

src/Core/Console/DatabaseStructure.php

@@ -79,6 +79,8 @@ HELP;
 				DBStructure::convertToInnoDB();
 				$output = ob_get_clean();
 				break;
+			default:
+				$output = 'Unknown command: ' . $this->getArgument(0);
 		}
 
 		$this->out($output);

src/Core/NotificationsManager.php

@@ -637,6 +637,8 @@ class NotificationsManager extends BaseObject
 	{
 		$knowyou = '';
 
+		$arr = [];
+
 		foreach ($intros as $it) {
 			// There are two kind of introduction. Contacts suggested by other contacts and normal connection requests.
 			// We have to distinguish between these two because they use different data.