win warning: fix probable precision lost in TClassEdit::STLKind
win warning: fix probable precision lost in TClassEdit::STLKind

unsigned char was used as length - means any fancy class name longer
than 256 characters will cause error. Original warning:

C:\build\workspace\root-pullrequests-build\root\core\foundation\src\TClassEdit.cxx(481):
warning C4267: '+=': conversion from 'size_t' to 'unsigned char',
possible loss of data
[C:\build\workspace\root-pullrequests-build\build\core\foundation\Foundation_Stage1.vcxproj]
karies/root,karies/root,root-mirror/root,olifre/root,olifre/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,karies/root,root-mirror/root,olifre/root,olifre/root,karies/root,karies/root,olifre/root,root-mirror/root,olifre/root,karies/root,root-mirror/root,olifre/root,root-mirror/root,karies/root,karies/root,olifre/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,olifre/root