Lazyness in getOrElse could cause disagreement between 6.0 and < 6.0 nodes

[kushti]

Something like Some(5).getOrElse(emptyColl(0)) would cause network split. V6 nodes would accept this script because the invalid operation (indexing empty coll) is never evaluated whereas v5 nodes would reject. Unless ErgoTree version is also >= 3 in which case old nodes would not evaluate script

Discovered by @SethDusek