Add missing cstdint header in meshloader.h

[nim65s]

Hi @ponchio,

You just merged #44, but I guess you missed my comment about about the same issue in another place: https://github.com/cnr-isti-vclab/corto/pull/44#issuecomment-2018972154

Here is a fix :)

[nim65s]

hum, while here, grep find others uint32_t in objload.h & tinyply.h. This didn't raise any issue for me, but I guess I can also include a fix for this.

[ponchio]

Thanks.