Issue title: Error generating windows10new package
 Issue body: I received the following error when generating a package for https://buoyantair.gitlab.io/modern-pomodoro/

512 is the default base image size that Microsoft Store requires....

>Failed. Status code 500, Error: , Details: System.InvalidOperationException: Couldn't find a suitable base image from which to generate all Windows package images. Base image sources: (https://buoyantair.gitlab.io/images/logo512x512.png, the base image from package options), (https://buoyantair.gitlab.io/images/logo.png, the largest square icon from web manifest), (https://buoyantair.gitlab.io/images/logo.png, largest icon from web manifest)
>   at Microsoft.PWABuilder.Windows.Chromium.Services.ImageGenerator.GetBaseImage(WindowsImages imageOptions, WebAppManifestContext webManifest) in D:\Dev\pwabuilder-windows-chromium\Services\ImageGenerator.cs:line 91
>   at Microsoft.PWABuilder.Windows.Chromium.Services.ImageGenerator.InvokePwabuilderImageGeneratorService(WindowsImages imageOptions, WebAppManifestContext webManifest) in D:\Dev\pwabuilder-windows-chromium\Services\ImageGenerator.cs:line 66
>   at Microsoft.PWABuilder.Windows.Chromium.Services.ImageGenerator.Generate(WindowsAppPackageOptions options, WebAppManifestContext manifest, String outputDirectory) in D:\Dev\pwabuilder-windows-chromium\Services\ImageGenerator.cs:line 47
>   at Microsoft.PWABuilder.Windows.Chromium.Services.WindowAppPackageCreator.GenerateZip(WindowsAppPackageOptions options) in D:\Dev\pwabuilder-windows-chromium\Services\WindowAppPackageCreator.cs:line 125
>   at Microsoft.PWABuilder.Windows.Chromium.Services.WindowAppPackageCreator.CreateAppPackage(WindowsAppPackageOptions options) in D:\Dev\pwabuilder-windows-chromium\Services\WindowAppPackageCreator.cs:line 63
>   at Microsoft.PWABuilder.Windows.Chromium.Controllers.MsixController.CreateAppPackage(WindowsAppPackageOptions options) in D:\Dev\pwabuilder-windows-chromium\Controllers\MsixController.cs:line 44
>   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
>   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
>   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
>   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
>   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
>   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
>   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
>   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
>   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
>   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
>   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
>
>HEADERS
>=======
>Accept: */*
>Accept-Encoding: gzip, deflate, br
>Accept-Language: en-US,en;q=0.9,fr;q=0.8
>Connection: close
>Content-Length: 1191
>Content-Type: application/json
>Host: pwabuilder-win-chromium-platform.centralus.cloudapp.azure.com
>Referer: https://www.pwabuilder.com/
>User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/843.577.1784 Safari/537.36
>origin: https://www.pwabuilder.com
>sec-fetch-site: cross-site
>sec-fetch-mode: cors
>sec-fetch-dest: empty
>
 Comments: 
 Comment 0: Hello buoyantair, thank you for opening an issue with us! 

I have automatically added a "needs triage" label to help get things started. Our team will investigate the issue and help solve it ASAP. Other community members may also look into the issue and provide feedback 🙌
{'source': 'GithubIssues', 'repo_name_with_owner': 'pwa-builder/PWABuilder', 'issue_id': 754091549, 'repo_stars': 1438.0}