UploadPack: Suppress resource warning about PackWriter

PackWriter is auto-closeable and should be opened in try-with-resource,
but this is not possible since the variable is being referenced in the
finally block before being explicitly closed there.

Suppress the warning and add an explanatory comment.

Change-Id: I161923f35142132234fd951c0146d3cb30920b7b
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java

@@ -1541,6 +1541,8 @@ public class UploadPack {
 		PackConfig cfg = packConfig;
 		if (cfg == null)
 			cfg = new PackConfig(db);
+		@SuppressWarnings("resource") // PackWriter is referenced in the finally
+										// block, and is closed there
 		final PackWriter pw = new PackWriter(cfg, walk.getObjectReader(),
 				accumulator);
 		try {