Fix a few db access crashes

src/Cache.cpp

@@ -787,6 +787,9 @@ Cache::isInitialized()
 std::string
 Cache::nextBatchToken()
 {
+        if (!env_.handle())
+                throw lmdb::error("Env already closed", MDB_INVALID);
+
         auto txn = lmdb::txn::begin(env_, nullptr, MDB_RDONLY);
         std::string_view token;
 
@@ -1816,6 +1819,9 @@ Cache::getTimelineRange(const std::string &room_id)
 std::optional<uint64_t>
 Cache::getTimelineIndex(const std::string &room_id, std::string_view event_id)
 {
+        if (event_id.empty() || room_id.empty())
+                return {};
+
         auto txn = lmdb::txn::begin(env_, nullptr, MDB_RDONLY);
 
         lmdb::dbi orderDb;

src/ChatPage.cpp

@@ -873,11 +873,14 @@ ChatPage::trySync()
 
         http::client()->sync(
           opts,
-          [this, since = cache::nextBatchToken()](const mtx::responses::Sync &res,
-                                                  mtx::http::RequestErr err) {
-                  if (since != cache::nextBatchToken()) {
-                          nhlog::net()->warn("Duplicate sync, dropping");
-                          return;
+          [this, since = opts.since](const mtx::responses::Sync &res, mtx::http::RequestErr err) {
+                  try {
+                          if (since != cache::nextBatchToken()) {
+                                  nhlog::net()->warn("Duplicate sync, dropping");
+                                  return;
+                          }
+                  } catch (const lmdb::error &e) {
+                          nhlog::db()->warn("Logged out in the mean time, dropping sync");
                   }
 
                   if (err) {