check for organizer image files if they are claimed to exist

[bridgetkromhout]

Expected behavior

If organizer images don't exist in the repo, don't try to show them (even if the config yml claims they exist).

Actual behavior

Broken images:

Reproduction Steps

Claim organizer image exists but don't put it in repo.

[mattstratton]

This likely should be extended to include speaker images, as well as sharing images (and some others that it hasn't occurred to me yet).

[bridgetkromhout]

Makes sense!

[somatorio]

i can help with that :)
just a question, what do you think is better: fail silently simply skipping the img tag or use errorf to make an error log and fail the build?

i'm tending to fail the build, but i think it's always better to ask when in doubt

[bridgetkromhout]

I am not sure we'd want to fail a build - I'd rather display a default image (which, if they don't like, they can replace).

[mattstratton]

We wouldn't fail the build if they left off an image - we fail it if they enter an image in the config but then the image is not there (i.e., I specify matt-stratton.png but forget to put the file in the repo, or misspell the file name, etc).

So I vote for failing the build. It's an error that is being caught, so it should fail.

[somatorio]

yeah, if the image is not set at data/events/yyyy-city.yml the theme already uses a default image as far as i could see :)