Bug 1695467 - Don't throw "Error: Can't find profile directory." when showing the profile manager. r=mossop

When the profile manager is showing (started with `--p`, we haven't yet selected a profile.
Don't pollute the console for this case.

Differential Revision: https://phabricator.services.mozilla.com/D250121

toolkit/components/xulstore/XULStore.sys.mjs

@@ -81,6 +81,9 @@ XULStore.prototype = {
       try {
         this._storeFile = Services.dirsvc.get("ProfDS", Ci.nsIFile);
       } catch (ex) {
+        if (Services.startup.startingUp) {
+          return;
+        }
         throw new Error("Can't find profile directory.");
       }
     }