Subject: [PATCH] Allow an empty mmap allocation total in heap_info

The allocator may satisfy all live allocations from the heap. A zero
mmap_used value is valid and depends on the worker allocation history.
Keep the heap and platform checks without requiring an mmap allocation.

--- a/tests/test_system.py
+++ b/tests/test_system.py
@@ -267,6 +267,7 @@
         if MACOS:
             assert m.mmap_used == 0  # not supported
         else:
-            assert m.mmap_used > 0
+            # A process can have no live mmap-backed malloc allocations.
+            assert m.mmap_used >= 0
         if WINDOWS:
             assert m.heap_count >= 0