Avoid re-propagation of shares during one propagation run

* fix was proposed by @nickvergessen

apps/files_sharing/lib/propagation/recipientpropagator.php

@@ -126,7 +126,13 @@ class RecipientPropagator {
 		});
 	}
 
+	protected $propagatingIds = [];
+
 	public function propagateById($id) {
+		if (isset($this->propagatingIds[$id])) {
+			return;
+		}
+		$this->propagatingIds[$id] = true;
 		$shares = Share::getAllSharesForFileId($id);
 		foreach ($shares as $share) {
 			// propagate down the share tree
@@ -141,5 +147,7 @@ class RecipientPropagator {
 				$watcher->writeHook(['path' => $path]);
 			}
 		}
+
+		unset($this->propagatingIds[$id]);
 	}
 }