multi_heap: ensure that malloc(0) return NULL pointer in any poisoning configuration

components/heap/multi_heap_poisoning.c

@@ -187,6 +187,10 @@ static bool verify_fill_pattern(void *data, size_t size, bool print_errors, bool
 
 void *multi_heap_aligned_alloc(multi_heap_handle_t heap, size_t size, size_t alignment)
 {
+    if (!size) {
+        return NULL;
+    }
+
     if (size > SIZE_MAX  - POISON_OVERHEAD) {
         return NULL;
     }
@@ -213,9 +217,14 @@ void *multi_heap_aligned_alloc(multi_heap_handle_t heap, size_t size, size_t ali
 
 void *multi_heap_malloc(multi_heap_handle_t heap, size_t size)
 {
+    if (!size) {
+        return NULL;
+    }
+    
     if(size > SIZE_MAX - POISON_OVERHEAD) {
         return NULL;
     }
+
     multi_heap_internal_lock(heap);
     poison_head_t *head = multi_heap_malloc_impl(heap, size + POISON_OVERHEAD);
     uint8_t *data = NULL;