(WIP) Fix snprintf with overlapping source and dest strings

[michaelortmann]

Found by: Will Buckner and michaelortmann
Patch by: michaelortmann
Fixes: #1061

One-line summary:
Fix snprintf with overlapping source and dest strings

Additional description (if needed):
This looks like another bug in the code:

eggdrop/src/mod/server.mod/server.c

Line 589 in 5182a22

egg_snprintf(newnicks, sizeof newnicks, ",%s", nick);

shouldnt nick be appended instead? %s,%s instead of ,%s?
Another line looks glitchy:

eggdrop/src/mod/server.mod/server.c

Line 583 in 5182a22

((9 + strlen(chan) + strlen(newnicks) + strlen(newnick) +

Here strlen(newnick) is calculated. But later:

eggdrop/src/mod/server.mod/server.c

Line 585 in 5182a22

if (newnick)

there is a check for newnick is NULL.
This doesnt make sense, does it?
We really need to come up with a good test for function parse_q() to make sure, the code works as expected. I think this function is buggy in its current state.
If there is indeed a bug it would effect eggdrop when optimize_kicks == 2 is set.
The alleged bug was introduced when optimize-kicks was added to eggdrop:
643554c#diff-917cd0562d3c81d827ab3b993432429b4433293a25e4090c1bda6823b705e4f2R539 in eggdrop 1.5.2

Test cases demonstrating functionality (if applicable):
I dont have real world test yet. Thats why this PR is still marked as WIP.