1.1.17: --help without -p runs the default pipeline instead of printing help #91

Since 1.1.17, running a script with -h / --help and no -p runs the default pipeline (the one with runIfOnlySpecified false) instead of printing the pipeline list. 1.1.16 prints the help.

Repro, same script under both versions:

#r "nuget: Fun.Build, 1.1.17" // works with 1.1.16

open Fun.Build

pipeline "Build" {
    stage "build" { run "echo building" }
    runIfOnlySpecified false
}

pipeline "Other" {
    stage "x" { run "echo other" }
    runIfOnlySpecified true
}

tryPrintPipelineCommandHelp ()

$ dotnet fsi build.fsx -- --help

• 1.1.16: prints Pipelines: Build (default), Other and the usage block.
• 1.1.17: runs the Build pipeline (echo building), then tryPrintPipelineCommandHelp prints the list afterwards.

Cause: #89 (Support run multiple pipelines in one execution) rewrote the dispatch in PipelineBuilder. Before, the isHelp check came first:

if isHelp then
    match pipelineIndex with
    | Some index when ... -> ctx.RunCommandHelp(verbose)
    | _ -> ()
else
    match pipelineIndex with
    | ...
    | None when not specified -> ctx.Run()

Now isHelp is only consulted inside the _ :: _ arm, so the no--p arm never sees it:

match pipelineIndexes with
| [] when not specified -> ctx.Run()   // runs on --help too
| [] -> ()
| _ :: _ -> ... if isHelp then ctx.RunCommandHelp(verbose) else ctx.Run()

Expected: [] when not specified && not isHelp -> ctx.Run(), so --help without -p only prints.