Fix string.strlen (dotnet/coreclr#22397)
Fix string.strlen (dotnet/coreclr#22397)

* Add explanation comment

Fixes #22393

Signed-off-by: dotnet-bot <03c4cb6107ae99956a7681f2c97ff7104809a2bd@microsoft.com>

ViktorHofer/corefx,ericstj/corefx,ericstj/corefx,BrennanConroy/corefx,wtgodbe/corefx,wtgodbe/corefx,ericstj/corefx,shimingsg/corefx,shimingsg/corefx,ptoonen/corefx,shimingsg/corefx,wtgodbe/corefx,ptoonen/corefx,wtgodbe/corefx,BrennanConroy/corefx,ericstj/corefx,ViktorHofer/corefx,ptoonen/corefx,ViktorHofer/corefx,ViktorHofer/corefx,shimingsg/corefx,wtgodbe/corefx,ViktorHofer/corefx,shimingsg/corefx,wtgodbe/corefx,shimingsg/corefx,ptoonen/corefx,ptoonen/corefx,shimingsg/corefx,BrennanConroy/corefx,ViktorHofer/corefx,ericstj/corefx,ViktorHofer/corefx,ericstj/corefx,ptoonen/corefx,ericstj/corefx,wtgodbe/corefx,ptoonen/corefx