linux-ramdump-parser-v2: Detect corruption in rb_tree

Red/Black trees are supposed to be trees, not directed cyclic graphs.
Sometimes trees in ramdumps may become corrupted though, resulting in
cycles. Detect these cycles in the tree to avoid looping forever.

Change-Id: I68cf018c6786b3c6947789a18c63c7a3a1f8d7bc