Defer Last Commit Info (#16467)

One of the biggest reasons for slow repository browsing is that we wait
until last commit information has been generated for all files in the
repository.

This PR proposes deferring this generation to a new POST endpoint that
does the look up outside of the main page request.

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/git/last_commit_cache.go

@@ -26,6 +26,9 @@ func (c *LastCommitCache) getCacheKey(repoPath, ref, entryPath string) string {
 
 // Put put the last commit id with commit and entry path
 func (c *LastCommitCache) Put(ref, entryPath, commitID string) error {
+	if c == nil || c.cache == nil {
+		return nil
+	}
 	log.Debug("LastCommitCache save: [%s:%s:%s]", ref, entryPath, commitID)
 	return c.cache.Put(c.getCacheKey(c.repoPath, ref, entryPath), commitID, c.ttl())
 }