Cancel previous list job on reloading folder
Cancel previous list job on reloading folder

Because the second list job may be started before the first one is finished (I've seen such cases and there's no guarantee they don't happen), making `finishLoading()` be emitted twice after `startLoading()`, which can have side effects. Moreover, redundant computations are prevented.

lxde/libfm-qt,lxde/libfm-qt