SettledResult isError fix

[livingos]

Fixes #161

Updates isError to handle missing FunctionError key as result of latest aws-sdk-php package.

[yassir3wad]

@aarondfrancis - Are you able to merge this PR?

[andrepg]

Thanks! I've applied this fix manually in my code and can confirm that it worked as expected.

I'm using Sidecar v0.7.0 and AWS versions SDK v3.351.12 (in production) and v3.351.6 (in development). In development we have a working code, but in production we don't.

Additionaly, I'm receiving just an Lambda Execution Exception for Wnx\SidecarBrowsershot\Functions\BrowsershotFunction: "Unknown error.". as a result of the execution.

Applying the PR code no longer throws an error.

[iAmKevinMcKee]

You can lock to 3.351.9 until this is merged.

[Akecel]

Thanks for that @livingos , I hope it will be merged quickly 💯

[patrickomeara]

To use this before it is merged set the following in your composer.json file.

{
    "require": {
        "hammerstone/sidecar": "dev-main#5836667 as 0.7.0",
    },
    "repositories": [
        {
            "type": "vcs",
            "url": "https://github.com/Erudus/sidecar"
        }
    ],
}

[alexbirtwell]

+1 for this fix to merge please.