fix(files): clear loadError on PDF success and fix streaming null-flash

- pdf-viewer: add setLoadError(null) in onLoadSuccess so the toolbar
  is not permanently hidden after a failed-then-successful PDF load
- file-viewer: consolidate streaming-mode rendering so the debounce
  period (before rendering=true) shows a skeleton instead of null

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/file-viewer.tsx

@@ -230,12 +230,10 @@ const IframePreview = memo(function IframePreview({
 
   if (renderError) return <PreviewError label='PDF' error={renderError} />
 
-  if (rendering && !streamingBuffer) {
-    return <div className='relative flex flex-1 overflow-hidden'>{PDF_PAGE_SKELETON}</div>
-  }
-
   if (streamingContent !== undefined) {
-    if (!streamingSource) return null
+    if (!streamingSource) {
+      return <div className='relative flex flex-1 overflow-hidden'>{PDF_PAGE_SKELETON}</div>
+    }
     return <PdfViewerCore key={streamingBufferSeq} source={streamingSource} filename={file.name} />
   }
 

apps/sim/app/workspace/[workspaceId]/files/components/file-viewer/pdf-viewer.tsx

@@ -259,6 +259,7 @@ export const PdfViewerCore = memo(function PdfViewerCore({ source, filename }: P
           onLoadSuccess={({ numPages }) => {
             setPageCount(numPages)
             setCurrentPage(1)
+            setLoadError(null)
             setIsDocumentReady(true)
           }}
           onLoadError={(err) => {