Fix asset catalog loading state showing "No assets found" while asset…

… selection filtering is loading. (#26291)

## Summary & Motivation

We added asset selection based filtering to the catalog page but need to
make sure the page properly waits for that filtering to occurring

## How I Tested These Changes

app-proxy

js_modules/dagster-ui/packages/ui-core/src/assets/AssetTable.tsx

@@ -80,7 +80,7 @@ export const AssetTable = ({
   }, [checkedDisplayKeys, displayKeys, groupedByDisplayKey]);
 
   const content = () => {
-    if (!assets.length) {
+    if (!assets.length && !isLoading) {
       if (assetSelection) {
         return (
           <Box padding={{top: 64}}>

js_modules/dagster-ui/packages/ui-core/src/assets/AssetsCatalogTable.tsx

@@ -255,7 +255,7 @@ export const AssetsCatalogTable = ({
     <AssetTable
       view={view}
       assets={displayed}
-      isLoading={filteredAssetsLoading}
+      isLoading={filteredAssetsLoading || fetchResult.loading}
       isFiltered={isFiltered}
       actionBarComponents={
         <div