Valid warnings from gcc including one takePicture() bug

[RalphCorderoy]

I'm building with arduino-cli compile -b arduino:avr:mega:cpu=atmega1280 -e --warnings all and gcc is spewing some valid warnings, including a nasty-looking non-void function without an explicit return.

uCamII/uCamII.cpp: In member function 'int UCAMII::attempt_sync()':
uCamII/uCamII.cpp:52:8: warning: unused variable 'cam_reply' [-Wunused-variable]
   byte cam_reply;
        ^~~~~~~~~
uCamII/uCamII.cpp:54:7: warning: unused variable 'last_reply' [-Wunused-variable]
   int last_reply = 0;
       ^~~~~~~~~~
uCamII/uCamII.cpp: In member function 'bool UCAMII::takePicture()':
uCamII/uCamII.cpp:177:1: warning: control reaches end of non-void function [-Wreturn-type]
 }

[dgtlmoon]

PR's are welcome :)