Silence non-externalized string warning in PackIndexV2

Change-Id: I8c94811972c593c898f6375178f250a2123d01c6
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackIndexV2.java

@@ -232,7 +232,7 @@ class PackIndexV2 extends PackIndex {
 		final int levelOne = objId.getFirstByte();
 		final int levelTwo = binarySearchLevelTwo(objId, levelOne);
 		if (levelTwo == -1)
-			throw new MissingObjectException(objId.copy(), "unknown");
+			throw new MissingObjectException(objId.copy(), "unknown"); //$NON-NLS-1$
 		return NB.decodeUInt32(crc32[levelOne], levelTwo << 2);
 	}