Address build warnings in ncurses example

[2bndy5]

Just a self-reminder really.

/home/runner/work/RF24Mesh/RF24Mesh/RF24Mesh/examples_RPi/ncurses/RF24Mesh_Ncurses_Master.cpp: In function ‘void drawTopology()’:
/home/runner/work/RF24Mesh/RF24Mesh/RF24Mesh/examples_RPi/ncurses/RF24Mesh_Ncurses_Master.cpp:219:56: warning: zero-length gnu_printf format string [-Wformat-zero-length]
  219 |     mvwprintw(topoPad, nodeY > 15 ? nodeY - 16 : 0, 0, "");
      |                                                        ^~
/home/runner/work/RF24Mesh/RF24Mesh/RF24Mesh/examples_RPi/ncurses/RF24Mesh_Ncurses_Master.cpp:241:25: warning: variable ‘y’ set but not used [-Wunused-but-set-variable]
  241 |                     int y = 0;
      |                         ^
/home/runner/work/RF24Mesh/RF24Mesh/RF24Mesh/examples_RPi/ncurses/RF24Mesh_Ncurses_Master.cpp:261:25: warning: variable ‘y’ set but not used [-Wunused-but-set-variable]
  261 |                     int y = 0;
      |                         ^
/home/runner/work/RF24Mesh/RF24Mesh/RF24Mesh/examples_RPi/ncurses/RF24Mesh_Ncurses_Master.cpp:281:25: warning: variable ‘y’ set but not used [-Wunused-but-set-variable]
  281 |                     int y = 0;
      |                         ^

[2bndy5]

/home/runner/work/RF24Mesh/RF24Mesh/RF24Mesh/examples_RPi/ncurses/RF24Mesh_Ncurses_Master.cpp:219:56: warning: zero-length gnu_printf format string [-Wformat-zero-length]
  219 |     mvwprintw(topoPad, nodeY > 15 ? nodeY - 16 : 0, 0, "");
      |                                                        ^~

I'm a little fuzzy on curses API. I think this warning implies that we could simply move the cursor to a position inside the specified "window" using mvwaddch() instead of a printf-like function.

-    mvwprintw(topoPad, nodeY > 15 ? nodeY - 16 : 0, 0, "");
+    mvwaddch(topoPad, nodeY > 15 ? nodeY - 16 : 0, 0, 0);