fix memory counting without custom allocator (vercel/turborepo#8102)

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Closes PACK-3044

crates/turbo-tasks-malloc/src/lib.rs

@@ -42,7 +42,7 @@ unsafe impl GlobalAlloc for TurboMalloc {
 
  unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
  let ret = mimalloc::MiMalloc.alloc_zeroed(layout);
- if ret.is_null() {
+ if !ret.is_null() {
  add(layout.size());
  }
  ret
@@ -82,7 +82,7 @@ unsafe impl GlobalAlloc for TurboMalloc {
 
  unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
  let ret = std::alloc::System.alloc_zeroed(layout);
- if ret.is_null() {
+ if !ret.is_null() {
  add(layout.size());
  }
  ret