fix(gatsby-plugin-sharp): error if we can't determine dimensions for image

[TylerBarnes]

This adds an error when dimensions for an image can't be determined. This happens when a file is corrupt. Previously the only error we got was TypeError: Cannot read property 'width' of null. I explored using another image dimensions package that gives us more meaning errors but it was giving other unrelated errors and seems like a risky change. Since the current package returns null if it can't find dimensions, I just error on null dimensions here and provide a generic message.

[TylerBarnes]

Prettier 2 added a bunch of extra changes on commit via husky. I can't make it not do that without downgrading prettier or removing husky, so I assume this is fine.

[vladar]

@TylerBarnes Looks like you have old Prettier (which uses new .prettierrc). Prettier 2.0 shouldn't add those changes (and that's why linting fails now). Run yarn and try again - it should help.

[pvdz]

Please don't merge Prettier related issues when it's due to Prettier 1 runtime on a Prettier 2 config.

[pvdz]

Turns out you can run /oss format 23156 if you run into this issue again, to fix the Prettier 1 vs 2 problems. As a workaround at least.

[pvdz]

(Consider my request for changes removed. Github won't let me, other than to accept it, but that's not what we want either, so meh. Ignore me in this PR :) )

[TylerBarnes]

Thanks @pvdz , I thought it was from our new config or something. Good to know I just need to use v2 instead

fixed by /oss format bot

[wardpeet]

Amazing!!!