wire: Use the last 1 to separate the hrp from bech32 strings

We were failing to decode some invoices because we were splitting on
the first `1`, not the last one. This would then result in the parsing
to break because 1 is not mapped in the u5 mapping.

Changelog-Fixed: pay: Parsing some bolt11 strings would fail if an amount is specified and the network mismatched.

common/bech32_util.c

@@ -69,7 +69,7 @@ bool from_bech32_charset(const tal_t *ctx,
 	bool upper = false, lower = false;
 	size_t datalen;
 
-	sep = memchr(bech32, '1', bech32_len);
+	sep = memrchr(bech32, '1', bech32_len);
 	if (!sep)
 		return false;
 

common/bolt12.c

@@ -141,7 +141,8 @@ static const u8 *string_to_data(const tal_t *ctx,
 		*fail = tal_fmt(ctx, "invalid bech32 string");
 		return NULL;
 	}
-	if (!streq(hrp, hrp_expected)) {
+
+	if (strlen(hrp) <= strlen(hrp_expected) || !strstarts(hrp, hrp_expected)) {
 		*fail = tal_fmt(ctx, "unexpected prefix %s", hrp);
 		data = tal_free(data);
 	} else