[BUG] Memory leaks

[MARK2580]

If you just open the texture browser in hammer (gmod) and view them all, the editor will take about 400-600 MB, because it unloads unused textures. If you do the same in hammer++ then it takes up more than 2gb of memory, maybe someone will think that re-generating the preview takes time, but the editor will not crash at the most inappropriate moment from memory overflow, which are available to a 32-bit application.