server: Fix SVG backwards compatibility (fixes #238)

Author: eliandoran

src/becca/entities/bnote.ts

@@ -1151,7 +1151,7 @@ class BNote extends AbstractBeccaEntity<BNote> {
             .map(row => new BAttachment(row));
     }
 
-    getAttachmentByTitle(title: string): BAttachment {
+    getAttachmentByTitle(title: string): BAttachment | undefined {
         // cannot use SQL to filter by title since it can be encrypted
         return this.getAttachments().filter(attachment => attachment.title === title)[0];
     }

src/routes/api/image.ts

@@ -44,9 +44,8 @@ function renderSvgAttachment(image: BNote | BRevision, res: Response, attachment
     let svg: string | Buffer = '<svg/>'
     const attachment = image.getAttachmentByTitle(attachmentName);
 
-    const content = attachment.getContent();
     if (attachment) {
-        svg = content;
+        svg = attachment.getContent();
     } else {
         // backwards compatibility, before attachments, the SVG was stored in the main note content as a separate key
         const contentSvg = image.getJsonContentSafely()?.svg;