throw an error rather than returning null on link preview failure

so that it is handled in the catch() block

ts/components/session/conversation/SessionCompositionBox.tsx

@@ -290,7 +290,7 @@ export class SessionCompositionBox extends React.Component<Props, State> {
     const { ignoredLink } = this.state;
 
     // Don't render link previews if quoted message or attachments are already added
-    if (stagedAttachments.length !== 0 && quotedMessageProps?.id) {
+    if (stagedAttachments.length !== 0 || quotedMessageProps?.id) {
       return <></>;
     }
     // we try to match the first link found in the current message

ts/components/session/conversation/SessionStagedLinkPreview.tsx

@@ -34,7 +34,7 @@ export const getPreview = async (
 ): Promise<null | GetLinkPreviewResult> => {
   // This is already checked elsewhere, but we want to be extra-careful.
   if (!window.Signal.LinkPreviews.isLinkSafeToPreview(url)) {
-    return null;
+    throw new Error('Link not safe for preview');
   }
 
   const linkPreviewMetadata = await LinkPreviewUtil.fetchLinkPreviewMetadata(
@@ -43,7 +43,7 @@ export const getPreview = async (
     abortSignal
   );
   if (!linkPreviewMetadata) {
-    return null;
+    throw new Error('Could not fetch link preview metadata');
   }
   const { title, imageHref, description, date } = linkPreviewMetadata;