compiler warnings in ncurses example

[2bndy5]

Opening this as a reminder (& for tracking). Current build of RF24Mesh_Ncurses_Master example is emitting the following warnings:

/path/to/RF24Mesh/examples_RPi/ncurses/RF24Mesh_Ncurses_Master.cpp: In function ‘void drawTopology()’:
/path/to/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, "");
      |                                                        ^~
/path/to/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;
      |                         ^
/path/to/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;
      |                         ^
/path/to/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]

duplicate of #241

I completely forgot I opened this, but #241 is more "involved".