Fix uncaugh exception at launch when indexedDB is forbidden

Possibly related to:
- https://www.reddit.com/r/uBlockOrigin/comments/atbjvg/web_pages_dont_load_in_waterfox_56271_64bit_with/

src/js/cachestorage.js

@@ -505,7 +505,10 @@
     };
 
     const clearIDB = function() {
+        try {
             indexedDB.deleteDatabase(STORAGE_NAME);
+        } catch(ex) {
+        }
     };
 
     return api;