issue: fix nil pointer dereference on plumb error

plumbserve() fails with a nil pointer dereference when it tries to
print errors via w.Err(). This happens because w is a dummy window
with a nil *acme.Win. This commit  replaces w.Err() calls in
plumbserve() with log.Printf(). It also extracts the plumbserve()
method out of *awin, given that the previous change removes this
dependency.

Fixes issue rsc#5.

issue/acme.go

@@ -59,30 +59,30 @@ func acmeMode() {
 		dummy.Look("all")
 	}
 
-	go dummy.plumbserve()
+	go plumbserve()
 
 	select {}
 }
 
-func (w *awin) plumbserve() {
+func plumbserve() {
 	fid, err := plumb.Open("githubissue", 0)
 	if err != nil {
-		w.Err(fmt.Sprintf("plumb: %v", err))
+		log.Printf("plumb: %v", err)
 		return
 	}
 	r := bufio.NewReader(fid)
 	for {
 		var m plumb.Message
 		if err := m.Recv(r); err != nil {
-			w.Err(fmt.Sprintf("plumb recv: %v", err))
+			log.Printf("plumb recv: %v", err)
 			return
 		}
 		if m.Type != "text" {
-			w.Err(fmt.Sprintf("plumb recv: unexpected type: %s\n", m.Type))
+			log.Printf("plumb recv: unexpected type: %s", m.Type)
 			continue
 		}
 		if m.Dst != "githubissue" {
-			w.Err(fmt.Sprintf("plumb recv: unexpected dst: %s\n", m.Dst))
+			log.Printf("plumb recv: unexpected dst: %s", m.Dst)
 			continue
 		}
 		// TODO use m.Dir
@@ -92,26 +92,26 @@ func (w *awin) plumbserve() {
 			project = data[len("/issue/"):]
 			i := strings.LastIndex(project, "/")
 			if i < 0 {
-				w.Err(fmt.Sprintf("plumb recv: bad text %q", data))
+				log.Printf("plumb recv: bad text %q", data)
 				continue
 			}
 			project, what = project[:i], project[i+1:]
 		} else {
 			i := strings.Index(data, "#")
 			if i < 0 {
-				w.Err(fmt.Sprintf("plumb recv: bad text %q", data))
+				log.Printf("plumb recv: bad text %q", data)
 				continue
 			}
 			project, what = data[:i], data[i+1:]
 		}
 		if strings.Count(project, "/") != 1 {
-			w.Err(fmt.Sprintf("plumb recv: bad text %q", data))
+			log.Printf("plumb recv: bad text %q", data)
 			continue
 		}
 		var plummy awin
 		plummy.prefix = "/issue/" + project + "/"
 		if !plummy.Look(what) {
-			w.Err(fmt.Sprintf("plumb recv: can't look %s%s", plummy.prefix, what))
+			log.Printf("plumb recv: can't look %s%s", plummy.prefix, what)
 		}
 	}
 }