memory leak in main_client

[pascal-niklaus]

I will at some stage prepare a PR to fix this, but want to document the issue here as a reminder

Describe the bug

In main.c, function main_client, clientdata is passed to the server.

• sometimes this a a part of argv, which does not need to be freed

• however, for the line argument, g_strjoin allocates a string that IMO is never freed

[bk138]

ACK, should be a strdup if part of argv and freed accordingly.