pkg/search: RLock index around GetBlobMeta

Because GetBlobMeta is a corpus read, we need to RLock around it.

Context: issue #750

Change-Id: I5b1e33d05b04aaecb0ad49f3af2d46d14b04dbfb

pkg/search/handler.go

@@ -95,10 +95,12 @@ func (sh *Handler) subscribeToNewBlobs() {
 	go func() {
 		ctx := context.Background()
 		for br := range ch {
+			sh.index.RLock()
 			bm, err := sh.index.GetBlobMeta(ctx, br)
 			if err == nil {
 				sh.wsHub.newBlobRecv <- bm.CamliType
 			}
+			sh.index.RUnlock()
 		}
 	}()
 }