AP_MultiHeap: initialize only if heap allocation succeeded

Signed-off-by: Rhys Mainwaring <[email protected]>

Author: srmainwaring

libraries/AP_MultiHeap/MultiHeap_malloc.cpp

@@ -36,9 +36,9 @@ void *MultiHeap::heap_create(uint32_t size)
 {
     struct heap *new_heap = (struct heap*)malloc(sizeof(struct heap));
     if (new_heap != nullptr) {
+        new_heap->magic = HEAP_MAGIC;
         new_heap->max_heap_size = size;
     }
-    new_heap->magic = HEAP_MAGIC;
     return (void *)new_heap;
 }