Fix error when initiating replication with a table that has no primary key

[Avalancs]

When trying to replicate a schema that has tables without primary keys I get an error like this:

2026-01-28 14:52:06 MainProcess INFO mysql_lib.py (844): Could not copy the table klwgc_fields_values. Excluding it from the replica.
2026-01-28 14:52:06 MainProcess CRITICAL mysql_lib.py (1597): init replica for source mariadb failed
Traceback (most recent call last):
  File "/work/pg_chameleon/scripts/chameleon.py", line 58, in <module>
    getattr(replica, args.command)()
  File "/work/pg_chameleon/pg_chameleon/lib/global_lib.py", line 371, in init_replica
    self.__init_mysql_replica()
  File "/work/pg_chameleon/pg_chameleon/lib/global_lib.py", line 381, in __init_mysql_replica
    self.mysql_source.init_replica()
  File "/work/pg_chameleon/pg_chameleon/lib/mysql_lib.py", line 1573, in init_replica
    self.__copy_tables()
  File "/work/pg_chameleon/pg_chameleon/lib/mysql_lib.py", line 838, in __copy_tables
    self.pg_engine.store_table(destination_schema, table, table_pkey, master_status)
  File "/work/pg_chameleon/pg_chameleon/lib/pg_lib.py", line 3883, in store_table
    if len(table_pkey) > 0:
       ^^^^^^^^^^^^^^^
TypeError: object of type 'NoneType' has no len()

By adding a check for None the replication works for me.