fix: initialize the uninitialized

[mariobodemann]

While building all demos I found that several colors are uninitialized, and where throwing an error when building.

Sample "error":

pimoroni-pico/examples/stellar_unicorn/stellar_lava_lamp.cpp: In function 'int main()':
pimoroni-pico/examples/stellar_unicorn/stellar_lava_lamp.cpp:128:27: error: 'bright_r' may be used uninitialized [-Werror=maybe-uninitialized]
  128 |           graphics.set_pen(bright_r, bright_g, bright_b);
      |           ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pimoroni-pico/examples/stellar_unicorn/stellar_lava_lamp.cpp:113:13: note: 'bright_r' was declared here
  113 |     uint8_t bright_r, bright_g, bright_b;
      |             ^~~~~~~~

I could have added the build flag for dismissing that warning, but I felt more explicit is better.

Let me know what you think.

[Gadgetoid]

Thank you, more explicit is indeed better. I try to build with Werror and Wall where possible, but we’re still targeting a pretty old compiler 😬