unittest: fix test for null tx input

Update the unittest that is meant to catch a transaction that is invalid
because it has a null input.  The old test failed not because of that
but because it was considered a coinbase with too large script.  This is
already checked with a different test, though.

The new test is *not* a coinbase since it has two inputs, but one of
them is null.  This really checks the corresponding code path in
CheckTransaction.

src/test/data/tx_invalid.json

@@ -64,9 +64,13 @@
 [[["0000000000000000000000000000000000000000000000000000000000000000", -1, "1"]],
 "01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff655151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151515151ffffffff010000000000000000015100000000", "P2SH"],
 
-["Null txin"],
-[[["0000000000000000000000000000000000000000000000000000000000000000", -1, "HASH160 0x14 0x02dae7dbbda56097959cba59b1989dd3e47937bf EQUAL"]],
-"01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff6e49304602210086f39e028e46dafa8e1e3be63906465f4cf038fbe5ed6403dc3e74ae876e6431022100c4625c675cfc5c7e3a0e0d7eaec92ac24da20c73a88eb40d09253e51ac6def5201232103a183ddc41e84753aca47723c965d1b5c8b0e2b537963518355e6dd6cf8415e50acffffffff010000000000000000015100000000", "P2SH"],
+["Null txin, but without being a coinbase (because there are two inputs)"],
+[[["0000000000000000000000000000000000000000000000000000000000000000", -1, "1"],
+  ["0000000000000000000000000000000000000000000000000000000000000100", 0, "1"]],
+"01000000020000000000000000000000000000000000000000000000000000000000000000ffffffff00ffffffff00010000000000000000000000000000000000000000000000000000000000000000000000ffffffff010000000000000000015100000000", "P2SH"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1"],
+  ["0000000000000000000000000000000000000000000000000000000000000000", -1, "1"]],
+"010000000200010000000000000000000000000000000000000000000000000000000000000000000000ffffffff0000000000000000000000000000000000000000000000000000000000000000ffffffff00ffffffff010000000000000000015100000000", "P2SH"],
 
 ["Same as the transactions in valid with one input SIGHASH_ALL and one SIGHASH_ANYONECANPAY, but we set the _ANYONECANPAY sequence number, invalidating the SIGHASH_ALL signature"],
 [[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0x21 0x035e7f0d4d0841bcd56c39337ed086b1a633ee770c1ffdd94ac552a95ac2ce0efc CHECKSIG"],