ZP-1244 use strcasecmp to compare CALDAV_PERSONAL and calendar id

If CALDAV_PERSONAL is defined with upper-case characters, a match would be impossible
Now, it will match by comparing case-insensitively.

Released under the Affero GNU General Public License (AGPL) version 3.

src/backend/caldav/caldav.php

@@ -150,7 +150,7 @@ class BackendCalDAV extends BackendDiff {
         $folder->displayname = $val->displayname;
         $folder->serverid = $id;
         if ($id[0] == "C") {
-            if (defined('CALDAV_PERSONAL') && strtolower(substr($id, 1)) == CALDAV_PERSONAL) {
+            if (defined('CALDAV_PERSONAL') && strcasecmp(substr($id, 1), CALDAV_PERSONAL) == 0) {
                 $folder->type = SYNC_FOLDER_TYPE_APPOINTMENT;
             }
             else {
@@ -158,7 +158,7 @@ class BackendCalDAV extends BackendDiff {
             }
         }
         else {
-            if (defined('CALDAV_PERSONAL') && strtolower(substr($id, 1)) == CALDAV_PERSONAL) {
+            if (defined('CALDAV_PERSONAL') && strcasecmp(substr($id, 1), CALDAV_PERSONAL) == 0) {
                 $folder->type = SYNC_FOLDER_TYPE_TASK;
             }
             else {