Add demo for issue 9798 (#13263)

Author: koppor

test-support/src/manual-tests/issue-9798/issue-9798.bib

@@ -0,0 +1,8 @@
+@Misc{minimal,
+  title = {Hello World},
+  file  = {:minimal.pdf:PDF},
+}
+
+@Comment{jabref-meta: databaseType:bibtex;}
+
+@Comment{jabref-meta: fileDirectory:.;}