webdav client crashes for secure connections if he doesn't have the right root certificate for ssl verification. For the moment I print at least a useful error message to the OC log and the Apache log

3rdparty/Sabre/DAV/Client.php

@@ -249,6 +249,7 @@ class Sabre_DAV_Client {
             // Automatically follow redirects
             CURLOPT_FOLLOWLOCATION => true,
             CURLOPT_MAXREDIRS => 5,
+        	//CURLOPT_SSL_VERIFYPEER	=> false,
         );
 
         switch ($method) {

apps/files_external/lib/webdav.php

@@ -96,6 +96,8 @@ class OC_FileStorage_DAV extends OC_Filestorage_Common{
 			$responseType=$response["{DAV:}resourcetype"]->resourceType;
 			return (count($responseType)>0 and $responseType[0]=="{DAV:}collection")?'dir':'file';
 		}catch(Exception $e){
+			error_log($e->getMessage());
+			\OCP\Util::writeLog("webdav client", \OCP\Util::sanitizeHTML($e->getMessage()), \OCP\Util::ERROR);
 			return false;
 		}
 	}