fix(JOIN): fix uninitialized variable bug and add code automation with .clang-format

[ygor-sena]

This PR:

1. addresses the issue of uninitialized variable flag raised by Valgrind which resulted from the case where the same client left a given channel and joined it again.
2. add code automation with .clang-format. To automatically style your code, run at project root the following command:
   find . -iname "*.hpp" -o -iname "*.cpp" | xargs clang-format -i

[gialexan]

ACK!