Fix over-eager layout size caching

Certain conditions caused the current size to get reused when it should've been
recomputed. This led to children sometimes only realizing that they wanted to
resize once the non dry run update came around, leading to some very strange
and incorrect layouts.

Author: stackotter

Sources/SwiftCrossUI/ViewGraph/ViewGraphNode.swift

@@ -169,7 +169,13 @@ public class ViewGraphNode<NodeView: View, Backend: AppBackend> {
             return cachedSize
         }
 
-        if dryRun, let currentSize,
+        // Attempt to cleverly reuse the current size if we can know that it
+        // won't change. We must of course be in a dry run, have a known
+        // current size, and must've run at least one proper dry run update
+        // since the last update cycle (checked via`!sizeCache.isEmpty`) to
+        // ensure that the view has been updated at least once with the
+        // current view state.
+        if dryRun, let currentSize, !sizeCache.isEmpty,
             ((Double(lastProposedSize.x) >= currentSize.maximumWidth
                 && Double(proposedSize.x) >= currentSize.maximumWidth)
                 || proposedSize.x == lastProposedSize.x)