Parity-ethereum: Add placeholder for broken token icons.

[bjornwgnr]

[ottodevs]

This is not alignment fault, is just the alt label for inexistent logo in SIM token, you should ask Simoleon team to implement a logo following the standard practices.

[tomusdrw]

We should replace missing images with some placeholder (both tokens and dapps).

[mattdorst]

I also think this should default to the placeholder ? mark icon used for other tokens without images.

[5chdn]

@mattdorst it has an icon but the link is broken. what you describe is already the case.

[agryaznov]

Isn't it some worse issue, which lets anybody to reproduce the trick done in SIM ERC20 contract to bother EVERY Ethereum account with unexpected token?

[5chdn]

@bjornwgnr fixed in 1.8.1

@agryaznov yes that's an issue, but we fixed it in 1.8.1