fix(http): race condition regression

The `race` condition directive was broken due to
a strict dependency on `threads > 0` for parallel
execution, causing templates with `race` directive
enabled but no explicit threads to fall back to
seq execution.

This regression was introduced in v3.2.0 (#4868),
which restricted parallel execution to only when
`payloads` were present.

Fixes #5713 to allow race conditions even w/o
explicit `payloads`, and add a default thread
count when race is enabled but threads is 0.

Signed-off-by: Dwi Siswanto <git@dw1.io>

pkg/protocols/http/request.go

@@ -501,7 +501,7 @@ func (request *Request) ExecuteWithResults(input *contextargs.Context, dynamicVa
 	}
 
 	// verify if parallel elaboration was requested
-	if request.Threads > 0 && len(request.Payloads) > 0 {
+	if request.Threads > 0 && (len(request.Payloads) > 0 || request.Race) {
 		return request.executeParallelHTTP(input, dynamicValues, callback)
 	}