Fixed IndexOutOfBoundsException that occurs when a repository doesn't

have commits within the requested time range.

Author: docbobo

src/com/gitblit/utils/ActivityUtils.java

@@ -85,7 +85,7 @@ public static List<Activity> getRecentActivity(List<RepositoryModel> models, int
 
 				// determine commit branch
 				String branch = objectId;
-				if (StringUtils.isEmpty(branch)) {
+				if (StringUtils.isEmpty(branch) && !commits.isEmpty()) {
 					List<RefModel> headRefs = allRefs.get(commits.get(0).getId());
 					List<String> localBranches = new ArrayList<String>();
 					for (RefModel ref : headRefs) {