PackIndexV2: fix possibly wrong check

According to http://stackoverflow.com/a/8381338, the maximum array
size is not Integer.MAX_VALUE, but Integer.MAX_VALUE - 8

Change-Id: I6ddc7470368acd20abf0885c53c89a982bb0f176
Signed-off-by: Marc Strapetz <marc.strapetz@syntevo.com>

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

@@ -116,7 +116,7 @@ class PackIndexV2 extends PackIndex {
 			}
 
 			final long nameLen = bucketCnt * Constants.OBJECT_ID_LENGTH;
-			if (nameLen > Integer.MAX_VALUE)
+			if (nameLen > Integer.MAX_VALUE - 8) // see http://stackoverflow.com/a/8381338
 				throw new IOException(JGitText.get().indexFileIsTooLargeForJgit);
 
 			final int intNameLen = (int) nameLen;