use region quarantine even if MAP_FIXED call fails

This is a more sensible way of handling an out-of-memory failure in this
edge case. It doesn't matter much in practice.

README.md

@@ -1008,7 +1008,7 @@ System calls used by all build configurations:
 * `mremap(old, old_size, new_size, MREMAP_MAYMOVE|MREMAP_FIXED, new)`
 * `munmap`
 * `write(STDERR_FILENO, buf, len)` (before aborting due to memory corruption)
-* `madvise(ptr, size, MADV_DONTNEED)` for `malloc_trim` with slab quarantines
+* `madvise(ptr, size, MADV_DONTNEED)`
 
 The main distinction from a typical malloc implementation is the use of
 getrandom. A common compatibility issue is that existing system call whitelists

h_malloc.c

@@ -839,10 +839,10 @@ static void regions_quarantine_deallocate_pages(void *p, size_t size, size_t gua
     }
 
     if (unlikely(memory_map_fixed(p, size))) {
-        deallocate_pages(p, size, guard_size);
-        return;
-    }
+        memory_purge(p, size);
+    } else {
         memory_set_name(p, size, "malloc large quarantine");
+    }
 
     struct quarantine_info target =
         (struct quarantine_info){(char *)p - guard_size, size + guard_size * 2};