ldns-blocking: fix another corner case with suffix matching

Ruleset:
```
*.example.com
ru.example.com
```

A query for `xru.example.com` would find `ru.example.com` as the longest
suffix. The expression didn't match since this is neither an exact match
nor a match that stops at a label.

However, this was ignoring the fact that there a different, shorter rule
could match.

This is pretty annoying, as keeping our promise to log the longest match
means that we need at least yet another lookup in that specific case.
Alternatively, the fpst lookup function could be specialized to stop at
labels, but that would defeat the point of this example plugin. So,
perform an extra lookup after striping the first (last, once the name is
reversed) label.

src/plugins/example-ldns-blocking/example-ldns-blocking.c

@@ -618,6 +618,24 @@ apply_block_domains(DCPluginDNSPacket *dcp_packet, Blocking * const blocking,
                 block = 1;
                 break;
             }
+            if (found_key_len < owner_str_len) {
+                size_t owner_part_len = owner_str_len;
+
+                while (owner_part_len > 0U && rev[owner_part_len] != '.') {
+                    owner_part_len--;
+                }
+                rev[owner_part_len] = 0;
+                if (owner_part_len > 0U && fpst_starts_with_existing_key
+                    (blocking->domains_rev, rev, owner_part_len,
+                     &found_key, &found_block_type)) {
+                    const size_t found_key_len = strlen(found_key);
+                    if (found_key_len <= owner_part_len &&
+                        (rev[found_key_len] == 0 || rev[found_key_len] == '.')) {
+                        block = 1;
+                        break;
+                    }
+                }
+            }
         }
         if (fpst_starts_with_existing_key(blocking->domains,
                                           owner_str, owner_str_len,