fixup: add switch stmt for P2SH-wrapped segwit input verification

P2SH-wrapped inputs are segwit inputs and should be eligible for
spending, however the spec as written didn't permit them

Reported-by: @SomberNight

Author: niftynei

02-peer-protocol.md

@@ -216,7 +216,10 @@ The receiving node:
       (and not removed) input's
     - `prevtx` is not a valid transaction
     - `prevtx_vout` is greater or equal to the number of outputs on `prevtx`
-    - the `scriptPubKey` of the `prevtx_out` output of `prevtx` is not exactly a 1-byte push opcode (for the numeric values 0 to 16) followed by a data push between 2 and 40 bytes
+    - if the `script_sig` is provided:
+	- and it is not exactly a 1-byte push opcode (for the numeric values `0` to `16`) followed by a data push between 2 and 40 bytes OR
+    - else:
+        - the `scriptPubKey` of the `prevtx_out` output of `prevtx` is not exactly a 1-byte push opcode (for the numeric values 0 to 16) followed by a data push between 2 and 40 bytes
       followed by a single push of 2 to 40 bytes
     - the `serial_id` is already included in the transaction
     - the `serial_id` has the wrong parity