[TASImage] prevent ROOT crash (#8185)
[TASImage] prevent ROOT crash (#8185)

* prevent ROOT crash

when fScaledImage->fImage is nullptr.
This happens in some corner cases, namely after a libpng error: Not a PNG file
Error in <TASImage::Paint>: image could not be rendered to display

* kPng is already the default parameter in the header

prevent reading a PNG if one expliclitly passes e.g. a parameter kBmp

* fix copy/paste error
olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root