Bad iframe breaks condenser

e.g.

<iframe src="https://cdn.dapplr.in/file/dapplr-images/cryptoanalysis/e5doOq0bevBtZac4u8mHvtxW7gmvVGlv.jpg" ></iframe>

Breaks everything. Other than breaking page loading, it can break post edit/submit page if gets into the draft.

The source of the problem comes from the "sanitize-html" library.

example post: https://hive.blog/test/@smarttrail/test-1596017654