fix prepare route when route renderer still pending (#190)

Author: tsnobip

.changeset/warm-hats-sneeze.md

@@ -0,0 +1,5 @@
+---
+"rescript-relay-router": patch
+---
+
+fix prepare route when route renderer still pending

packages/rescript-relay-router/src/RelayRouter__Internal__DeclarationsSupport.res

@@ -351,6 +351,9 @@ let makePrepareAssets = (~loadedRouteRenderers, ~prepareDisposeTimeout): prepare
               preparedProps,
             ),
           )
+        | (Some(Pending(promise)), Loaded(_)) =>
+          suspend(promise)
+          React.null
         | _ =>
           Console.log("Warning: Invalid state")
           React.null