Fix gc's usage of progress monitor

Change-Id: I8dcdf0b83e91e6132dc490e8ec53818220773c94
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/storage/file/GC.java

@@ -137,6 +137,7 @@ public class GC {
 	 * @throws IOException
 	 */
 	public Collection<PackFile> gc() throws IOException {
+		pm.start(6 /* tasks */);
 		packRefs();
 		// TODO: implement reflog_expire(pm, repo);
 		Collection<PackFile> newPacks = repack();
@@ -262,6 +263,7 @@ public class GC {
 		if (fanout != null && fanout.length > 0) {
 			pm.beginTask(JGitText.get().pruneLooseUnreferencedObjects,
 					fanout.length);
+			try {
 				for (String d : fanout) {
 					pm.update(1);
 					if (d.length() != 2)
@@ -291,6 +293,9 @@ public class GC {
 						}
 					}
 				}
+			} finally {
+				pm.endTask();
+			}
 		}
 		if (deletionCandidates.isEmpty())
 			return;