`dotnet format` throws when multiple solutions are present in the current directory

```
D:\Roslyn>dotnet format
Unhandled exception: System.IO.FileNotFoundException: Multiple MSBuild solution files found in 'D:\R4\'. Specify which to use with the argument.
at Microsoft.CodeAnalysis.Tools.Workspaces.MSBuildWorkspaceFinder.FindMatchingFile(String searchBase, Func`2 fileSelector, String multipleFilesFoundError)
at Microsoft.CodeAnalysis.Tools.Workspaces.MSBuildWorkspaceFinder.FindWorkspace(String searchDirectory, String workspacePath)
at Microsoft.CodeAnalysis.Tools.Workspaces.MSBuildWorkspaceFinder.FindWorkspace(String searchDirectory, String workspacePath)
at Microsoft.CodeAnalysis.Tools.FormatCommandCommon.ParseWorkspaceOptions(ParseResult parseResult, FormatOptions formatOptions)
at Microsoft.CodeAnalysis.Tools.Commands.RootFormatCommand.FormatCommandDefaultHandler.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__DisplayClass17_0.<b__0>d.MoveNext()
--- End of stack trace from previous location ---
at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass12_0.<b__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__DisplayClass19_0.<b__0>d.MoveNext()
--- End of stack trace from previous location ---
at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<b__18_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.<b__5_0>d.MoveNext()
--- End of stack trace from previous location ---
at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass8_0.<b__0>d.MoveNext()
```