mod_c2s_limit_sessions: Fix check when it's the first connection Creation of the sessions[username] entry happens after the "pre-resource-bind" event, before the "resource-bind" event. Thus, for a users first connection, it may not exist. This led to an 'attempt to index a nil value' error, fixed here.

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summary: Set process name to prosody
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This module sets the process name to `prosody` so it shows up as such
instead of `lua` in process management tools.

To use this module, you'll need the proctitle Lua library:
<https://github.com/hoelzro/lua-proctitle>