talksapp: do not fail if caching presentation fails

fixes #438

Change-Id: I5d70552c3cc609c88825ca652b705fd137425866
Reviewed-on: https://go-review.googlesource.com/27561
Reviewed-by: Chris Broadfoot <cbro@golang.org>

talksapp/main.go

diff --git a/talksapp/main.go b/talksapp/main.go
index 0626494..ec8c703 100644
--- a/talksapp/main.go
+++ b/talksapp/main.go
@@ -213,7 +213,8 @@
 		Value:      buf.Bytes(),
 		Expiration: time.Hour,
 	}); err != nil {
-		return err
+		log.Errorf(ctx, "Could not cache presentation %s: %v", importPath, err)
+		return nil
 	}
 
 	writeHTMLHeader(w, 200)