No picon url defaults back to getting screen grab

[leaskovski]

• openwebifpy version: 3.1.1
• Python version: 3.7
• Operating System: Raspbian Buster (Home Assistant venv)

When using the engima2 integration in Home Assistant, which uses the 3.1.1 version of this component, when configuring to use a picon image for the channel, this means that a picon url is built and a picon image is tried to be retrieved. If, for some reason the picon url cannot be retrieved, the component falls back to getting a screen grab. This maybe ok for some boxes, but for my enigma2 box, it causes a 1 seconds freeze/slow down.

It would be preferable if this fall back was configurable to not grab a screen grab.

[fbradyirl]

Fixed in commit.

1f303b4