Slideshow delay allows zero delay value

[ianorlin]

lximageallows a slidshow delay of zero to be set in the prefrences which doesn't really make a sensible slideshow that changes pictures and instead ends up using 100 percent cpu for a single core switching the images as fast as the cpu goes which could lead to someone thinking they are clever than quickly running out of battery on a laptop or overheating there system maybe. I think a fix might be to take the maximum of 1 and settings.slideShowInterval() in lximage-qt/src/prefrences-dialog on line 40. Or someone presses a key and hits 0 on accident and starts the slideshow would result in a system using 100 percent cpu.