work/exec throw an error when buildP is negative

Fixed a problem where an error would not occur
when a negative value was specified for the p flag.

Fixes #46686

src/cmd/go/go_test.go

@@ -2880,3 +2880,13 @@ func TestMissingCC(t *testing.T) {
 		t.Error(`clearing "PATH" causes "net" to be stale`)
 	}
 }
+
+// Issue 46686
+func TestInvalidValueForFlagP(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+	tg.tempDir("src")
+	tg.setenv("GOPATH", tg.path("."))
+	tg.runFail("build", "-p=-1")
+}

src/cmd/go/internal/work/exec.go

@@ -180,6 +180,12 @@ func (b *Builder) Do(ctx context.Context, root *Action) {
 	if cfg.BuildN {
 		par = 1
 	}
+
+	if par <= 0 {
+		fmt.Fprintf(os.Stderr, "go: the number of builds should be positive: %v\n", par)
+		base.SetExitStatus(1)
+	}
+
 	for i := 0; i < par; i++ {
 		wg.Add(1)
 		go func() {