bug(PdfViewer): do not render when url is empty

[ArgoZhang]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

do not render when url is empty

Expected Behavior

none

Interactive render mode

Interactive Server (Interactive server-side rendering (interactive SSR) using Blazor Server)

Steps To Reproduce

none

Exceptions (if any)

No response

.NET Version

NET9.0

Anything else?

No response

[bb-auto]

@ArgoZhang Thank you for filing this issue. In order for us to investigate this issue, please provide a minimalistic repro project that illustrates the problem.