[Bug] Thumbnails are not created for high res files that have smaller size than thumbnail_max option

[maplee0]

https://github.com/lxde/libfm/commit/00120b795a811ae70db89dde5021461658f2880f

it resulted in thumbnails were not created for jpg files that have width of 3000px and height of 3000px and file size 2.9 MB. However, thumbnail_max option in the pcmanfm settings was set to 4096 KB.