fix empty timeline on initial load (#2586)

app/src/main/java/com/keylesspalace/tusky/components/timeline/viewmodel/CachedTimelineViewModel.kt

@@ -267,8 +267,11 @@ class CachedTimelineViewModel @Inject constructor(
         }
     }
 
-    override fun invalidate() {
-        currentPagingSource?.invalidate()
+    override suspend fun invalidate() {
+        // invalidating when we don't have statuses yet can cause empty timelines because it cancels the network load
+        if (db.timelineDao().getStatusCount(accountManager.activeAccount!!.id) > 0) {
+            currentPagingSource?.invalidate()
+        }
     }
 
     companion object {

app/src/main/java/com/keylesspalace/tusky/components/timeline/viewmodel/NetworkTimelineViewModel.kt

@@ -249,7 +249,7 @@ class NetworkTimelineViewModel @Inject constructor(
         currentSource?.invalidate()
     }
 
-    override fun invalidate() {
+    override suspend fun invalidate() {
         currentSource?.invalidate()
     }
 

app/src/main/java/com/keylesspalace/tusky/components/timeline/viewmodel/TimelineViewModel.kt

@@ -174,7 +174,7 @@ abstract class TimelineViewModel(
     abstract fun fullReload()
 
     /** Triggered when currently displayed data must be reloaded. */
-    protected abstract fun invalidate()
+    protected abstract suspend fun invalidate()
 
     protected fun shouldFilterStatus(statusViewData: StatusViewData): Boolean {
         val status = statusViewData.asStatusOrNull()?.status ?: return false