Steps to reproduce:
1.) Create a new picture in gimp.
2.) Select in gimp a small region of approximately 15x25 pixels.
3.) Call gmic and select filter "Deformations->Cartesian transform".
4.) Call "zoom in" function in preview three times. Gmic will display "preview may be inaccurate" warning.
5.) Now just call "zoom in" function at least five times and gmic will crash with following message:
Calling error for procedure 'gimp-drawable-sub-thumbnail': Procedure 'gimp-drwable-sub-tumbnail'
has been called with value '0' for argument 'src-width' (#3, type GimpInt32). This value is
out of range.
[instance(0,0,0,0,0000000000000000,non-shared)] CImg::crop(): Empty instance.