Pull up following revision(s) (requested by maxv in ticket #1332):

sys/uvm/uvm_mmap.c: revision 1.173

Change 'npgs' from int to size_t. Otherwise the 64bit->32bit conversion
could lead to npgs=0, which is not expected. It later triggers a panic
in uvm_vsunlock().

Found by TriforceAFL (Akul Pillai).

(martin)