wallet: fix logic for finding first block.

Over 20 years a professional C programmer, still can't count from zero!

Fixes: #709
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

wallet/wallet.c

@@ -632,8 +632,8 @@ u32 wallet_channels_first_blocknum(struct wallet *w)
 		     OPENINGD, CLOSINGD_COMPLETE);
 
 	err = sqlite3_step(stmt);
-	if (err == SQLITE_ROW && sqlite3_column_type(stmt, 1) != SQLITE_NULL)
-		first_blocknum = sqlite3_column_int(stmt, 1);
+	if (err == SQLITE_ROW && sqlite3_column_type(stmt, 0) != SQLITE_NULL)
+		first_blocknum = sqlite3_column_int(stmt, 0);
 	else
 		first_blocknum = UINT32_MAX;