cmd/go/internal/par: fix cond crash

Change-Id: Ie35a1699ce669571791c625cd6e212634e73f869
Reviewed-on: https://go-review.googlesource.com/119336
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/vendor/cmd/go/internal/par/work.go b/vendor/cmd/go/internal/par/work.go
index 31c29b1..44a4e8c 100644
--- a/vendor/cmd/go/internal/par/work.go
+++ b/vendor/cmd/go/internal/par/work.go
@@ -26,7 +26,6 @@
 func (w *Work) init() {
 	if w.added == nil {
 		w.added = make(map[interface{}]bool)
-		w.wait.L = &w.mu
 	}
 }
 
@@ -61,6 +60,7 @@
 
 	w.running = n
 	w.f = f
+	w.wait.L = &w.mu
 
 	for i := 0; i < n-1; i++ {
 		go w.runner()