pukkandan 337e0c62f8 [embedthumbnail] Correctly escape filename ...

Closes #352
The approach in [1] is faulty as can be seen in the test cases
1. bff857a8af

2021-05-29 02:31:14 +05:30

..

foo_%d.webp

[embedthumbnail] Correctly escape filename

2021-05-29 02:31:14 +05:30