Fix threshold test in VS2019 Debug build.
Fix threshold test in VS2019 Debug build.

The setup code for the test creates a buffer using vector's reserve.  This works for the release build but in debug build VS uses checked iterators which causes an error to be generated.  Changed reserve to resize.
huycn/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,nu-book/zxing-cpp,huycn/zxing-cpp,huycn/zxing-cpp,nu-book/zxing-cpp,nu-book/zxing-cpp