#187 process.c: avoid negative number of children

[negan07]

The number_of_children child connections number becomes negative (-1) at server startup due to signal handlers treatments on minidlna.c init()

Opening the webserver status page with no clients connected the opening connection shows -1 even if client list show 0 for all in the columns.

When connecting the first client, its own connections column goes to 1 and total goes to 0, and so on always one count behind.

attachment simply allows: number_of_children-- only if not 0