crash on invalid files with undefined bit depth

[novomesk]

Hello,

@easymodo uses qt-heif-image-plugin in his qimgv viewer.

Following file causes it to crash: http://188.121.162.14/libheif/oom-4a28c25c8f67b5c19ab742af5296370989f1f5ed.heif

I believe this crash is avoidable, files with undefined bit depth could be rejected by the plug-in.