[mkbundle] Fix check for dos2unix

This fixes the command to check for dos2unix and makes mkbundle usable again with mingw.
We need first to redirect the standard input, otherwise the check always fails with an InvalidOperationException and set CreateNoWindow=false to avoid spawning a new window.
Merge pull request #1288 from ylatuya/patch-2

[mkbundle] Fix check for dos2unix