Make sure EMU fails gracefully when a file is not found

[atruskie]

In the case where a target is specified as an absolute path, and the path for some reason is missing, then we fail with a stack trace.

• Fail with a coherent error message
• Ensure exit code is set appropriately

Note: this may be part of a larger error handling epic we have to deal with.

Stack trace we saw in prod:

 Failed running EMU: Unhandled exception: System.IO.FileNotFoundException: Could not find file '/data/harvester_to_do/harvest_1/20220317_61/243/156/20201202_AAO/20201202T100000+1000_REC.flac'. File name: '/data/harvester_to_do/harvest_1/20220317_61/243/156/20201202_AAO/20201202T100000+1000_REC.flac' at Interop.ThrowExceptionForIoErrno(ErrorInfo , String , Boolean , Func`2 ) at Interop.CheckIo(Error , String , Boolean , Func`2 ) at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String , OpenFlags , Int32 ) at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String , FileMode , FileAccess , FileShare , FileOptions , Int64 ) at System.IO.Strategies.OSFileStreamStrategy..ctor(String , FileMode , FileAccess , FileShare , FileOptions , Int64 ) at System.IO.Strategies.UnixFileStreamStrategy..ctor(String , FileMode , FileAccess , FileShare , FileOptions , Int64 ) at System.IO.Strategies.FileStreamHelpers.ChooseStrategyCore(String , FileMode , FileAccess , FileShare , FileOptions , Int64 ) at System.IO.Strategies.FileStreamHelpers.ChooseStrategy(FileStream , String , FileMode , FileAccess , FileShare , Int32 , FileOptions , Int64 ) at System.IO.FileStream..ctor(String , FileMode , FileAccess , FileShare , Int32 , FileOptions , Int64 ) at System.IO.FileStream..ctor(String , FileMode , FileAccess , FileShare , Int32 , FileOptions ) at System.IO.FileStream..ctor(String , FileMode , FileAccess , FileShare , Int32 , Boolean ) at System.IO.FileStream..ctor(String , FileMode , FileAccess , FileShare ) at System.IO.File.OpenRead(String ) at System.IO.Abstractions.FileWrapper.OpenRead(String path) at Emu.Fixes.FrontierLabs.MetadataDurationBug.CheckAffectedAsync(String file) in /app/src/Emu/Fixes/FrontierLabs/MetadataDurationBug.cs:line 40 at Emu.Fixes.FrontierLabs.MetadataDurationBug.ProcessFileAsync(String file, DryRun dryRun) in /app/src/Emu/Fixes/FrontierLabs/MetadataDurationBug.cs:line 49 at Emu.FixApply.ApplyFixAsync(String file, DryRun dryRun, IFixOperation operation, CheckResult checkResult) in /app/src/Emu/Commands/Fix/Apply/FixApply.cs:line 284 at Emu.FixApply.ProcessFile(String file, DryRun dryRun, ICheckOperation[] operations) in /app/src/Emu/Commands/Fix/Apply/FixApply.cs:line 187 at Emu.FixApply.InvokeAsync(InvocationContext context) in /app/src/Emu/Commands/Fix/Apply/FixApply.cs:line 90 at Emu.Extensions.System.CommandLine.CommandLineExtensions.<>c__DisplayClass0_0`3.<b__1>d.MoveNext() in /app/src/Emu/Extensions/System/CommandLine/CommandLineExtensions.cs:line 73 --- End of stack trace from previous location --- at System.CommandLine.Invocation.CommandHandler.GetExitCodeAsync(Object value, InvocationContext context) at System.CommandLine.Invocation.ModelBindingCommandHandler.InvokeAsync(InvocationContext context) at System.CommandLine.Invocation.InvocationPipeline.<>c__DisplayClass4_0.<b__0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass23_0.<b__0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Hosting.HostingExtensions.<>c__DisplayClass1_0.<b__0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass16_0.<b__0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass27_0.<b__1>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass25_0.<b__0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<b__24_0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass22_0.<b__0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass11_0.<b__0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<b__10_0>d.MoveNext() --- End of stack trace from previous location --- at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass14_0.<b__0>d.MoveNext()