Fix interval midpoint calculation in vulkan (#46839)

Summary:
Pull Request resolved: #46839

Interval midpoint calculations can overflow (integers). This fixes such an instance.

Test Plan: Standard test rig.

Reviewed By: drdarshan

Differential Revision: D24392545

fbshipit-source-id: 84c81802165bb8084e2d54c9f3755f39143a5b00

aten/src/ATen/native/vulkan/api/vk_mem_alloc.h

@@ -4594,7 +4594,7 @@ static IterT VmaBinaryFindFirstNotLess(IterT beg, IterT end, const KeyT &key, co
     size_t down = 0, up = (end - beg);
     while(down < up)
     {
-        const size_t mid = (down + up) / 2;
+        const size_t mid = down + (up - down) / 2; //Overflow-safe midpoint calculation
         if(cmp(*(beg+mid), key))
         {
             down = mid + 1;