Fix adding state events to the database (#3133)

When we're adding state to the database, we check which eventNIDs are
already in a block, if we already have that eventNID, we remove it from
the list. In its current form we would skip over eventNIDs in the case
we already found a match (we're decrementing `i` twice)
My theory is, that when we later get the state blocks, we are receiving
"too many" eventNIDs (well, yea, we stored too many), which may or may
not can result in state resets when comparing different state snapshots.
(e.g. when adding state we stored a eventNID by accident because we
skipped it, later we add more state and are not adding it because we
don't skip it)

roomserver/storage/shared/storage.go

@@ -282,17 +282,17 @@ func (d *Database) addState(
 		var found bool
 		for i := len(state) - 1; i >= 0; i-- {
 			found = false
+		blocksLoop:
 			for _, events := range blocks {
 				for _, event := range events {
 					if state[i].EventNID == event {
 						found = true
-						break
+						break blocksLoop
 					}
 				}
 			}
 			if found {
 				state = append(state[:i], state[i+1:]...)
-				i--
 			}
 		}
 	}