Don't enqueue multiple syncs of collection, which is being synced

Fix logic error that allowed queuing multiple syncs of the collection,
for which an active sync is ongoing. Instead the logic should only
allow to queue one additional sync besides the one currently in
operation.

Signed-off-by: Krzysztof Nowicki <krissn@op.pl>

resources/ews/ewsresource.cpp

@@ -352,10 +352,11 @@ void EwsResource::queueFetchItemsJob(const Akonadi::Collection &col, std::functi
     qCDebugNC(EWSRES_LOG) << QStringLiteral("Enqueuing sync for collection ") << col;
 
     const auto queueEmpty = mFetchItemsJobQueue.empty();
-    if (!queueEmpty) {
-        for (const auto &item : std::as_const(mFetchItemsJobQueue)) {
-            // Don't enqueue the same collection twice, unless it's for the currently synced collection.
-            if (item.col != mFetchItemsJobQueue.head().col && item.col == col) {
+    if (mFetchItemsJobQueue.count() > 1) {
+        // Don't enqueue the same collection id, type pair twice, except for the first element,
+        // which belongs to the collection being synced right now.
+        for (const auto &item : std::as_const(mFetchItemsJobQueue).mid(1)) {
+            if ((item.col == col) && (item.type == type)) {
                 qCDebugNC(EWSRES_LOG) << QStringLiteral("Sync already queued - skipping");
                 return;
             }