fix(psalm): Fix some unrelated psalm issues

Signed-off-by: Carl Schwan <carlschwan@kde.org>

Author: CarlSchwan

lib/private/Authentication/WebAuthn/Manager.php

@@ -141,7 +141,7 @@ public function finishRegister(PublicKeyCredentialCreationOptions $publicKeyCred
 	}
 
 	private function stripPort(string $serverHost): string {
-		return preg_replace('/(:\d+$)/', '', $serverHost);
+		return preg_replace('/(:\d+$)/', '', $serverHost) ?? '';
 	}
 
 	public function startAuthentication(string $uid, string $serverHost): PublicKeyCredentialRequestOptions {

lib/private/Avatar/Avatar.php

@@ -191,7 +191,7 @@ protected function generateAvatar(string $userDisplayName, int $size, bool $dark
 		$data = ob_get_contents();
 		ob_end_clean();
 
-		return $data;
+		return $data ?: '';
 	}
 
 	/**