Set m_seed in build_from_hashes instead of build_from_keys

Not setting the seed in build_from_hashes prevents users of the crate from
using it, as they otherwise cannot set the seed

include/builders/internal_memory_builder_single_phf.hpp

@@ -27,7 +27,6 @@ struct internal_memory_builder_single_phf {
             }
             throw seed_runtime_error();
         }
-        m_seed = config.seed;
         return build_from_hashes(hash_generator<RandomAccessIterator>(keys, m_seed), num_keys,
                                  config);
     }
@@ -54,6 +53,7 @@ struct internal_memory_builder_single_phf {
                                    ? (std::ceil((config.c * num_keys) / std::log2(num_keys)))
                                    : config.num_buckets;
 
+        m_seed = config.seed;
         m_num_keys = num_keys;
         m_table_size = table_size;
         m_num_buckets = num_buckets;