fix: prevent signer overwrite when adding multiple signers to envelope

Use count of existing signers as next index instead of complex calculation
that could result in same index being reused, causing signers to overwrite
each other when loading LibreSign signers without certificate data.

Signed-off-by: Vitor Mattos <[email protected]>

Author: vitormattos

lib/Service/File/SignersLoader.php

@@ -64,9 +64,8 @@ public function loadLibreSignSigners(
 				if (!empty($found)) {
 					$index = key($found);
 				} else {
-					$totalSigners = count($signers);
-					$totalCert = count($certData);
-					$index = $totalSigners > $totalCert ? $totalCert : $totalSigners - 1;
+					// Find next available index
+					$index = count($fileData->signers);
 				}
 			} else {
 				$index = 0;