godoc: bring back "indexing in progress" message

A wrongly nested if prevented the message from appearing.

Fixes #1420.

R=r, r2
CC=golang-dev
https://golang.org/cl/3987043

src/cmd/godoc/godoc.go

@@ -1172,7 +1172,8 @@ func lookup(query string) (result SearchResult) {
 		lookupStr = prefix
 	}
 
-	if index, timestamp := searchIndex.get(); index != nil {
+	index, timestamp := searchIndex.get()
+	if index != nil {
 		// identifier search
 		index := index.(*Index)
 		result.Hit, result.Alt, err = index.Lookup(lookupStr)
@@ -1188,12 +1189,16 @@ func lookup(query string) (result SearchResult) {
 		const max = 10000 // show at most this many fulltext results
 		result.Found, result.Textual = index.LookupRegexp(lookupRx, max+1)
 		result.Complete = result.Found <= max
+	}
 
 	// is the result accurate?
 	if _, ts := fsModified.get(); timestamp < ts {
+		// The index is older than the latest file system change
+		// under godoc's observation. Indexing may be in progress
+		// or start shortly (see indexer()).
 		result.Alert = "Indexing in progress: result may be inaccurate"
 	}
-	}
+
 	return
 }