vm_phys_enq_range: no alignment assert for npages==0

[dougm]

Summary

Do not assume that when vm_phys_enq_range is passed npages==0 that the vm_page argument is valid in any way, much less that it has a page-aligned address. Just don't look at it. Assert nothing about it.

[• karels]

This looks right to me, and works on my system. Perhaps a comment in the block before the routine would be appropriate, saying that npages may be zero, in which case nothing should be done.

[dougm]

Add to the preface comment that npages may be zero.