reload: Fix tracebacks on browsers without local storage.

This fixes an issue where browsers without local storage (aka the
Zulip ancient QT-based desktop app) would throw an exception trying to
reload in modern Zulip.

static/js/reload.js

@@ -15,6 +15,19 @@ exports.is_in_progress = function () {
 };
 
 function preserve_state(send_after_reload, save_pointer, save_narrow, save_compose) {
+    if (!localstorage.supported()) {
+        // If local storage is not supported by the browser, we can't
+        // save the browser's position across reloads (since there's
+        // no secure way to pass that state in a signed fashion to the
+        // next instance of the browser client).
+        //
+        // So we jure return here and let the reload proceed without
+        // having preserved state.  We keep the hash the same so we'll
+        // at least save their narrow state.
+        blueslip.log("Can't preserve state; no local storage.");
+        return;
+    }
+
     if (send_after_reload === undefined) {
         send_after_reload = 0;
     }