Fix a warning

[ebachard]

[ 12%] Building CXX object CMakeFiles/prlib.dir/src/BlurDetection.cpp.o
$HOME/Devel/MATHS/PRLib/src/BlurDetection.cpp: In function ‘bool prl::isBlurred(const cv::Mat&, prl::BlurDetectionAlgo)’:
$HOME/Devel/MATHS/PRLib/src/BlurDetection.cpp:97:1: warning: control reaches end of non-void function [-Wreturn-type]
   97 | }

The warning is caused by nothing is returned once the right algo is found. I'd suggest to return false when no algo is found, thus a false value returned will help top detect a problem. And the warning will automaticaly vanish at build time, what cannot be bad :-)

Feel free to accept (or not) this little change under MIT license, (or whatever you need).

Thanks again for sharing your code !

With best regards,
Eric Bachard