Improving the code

In the mpool_alloc and mpool_calloc functions, I observed duplicate code
 segments. Consequently, I refactored the mpool_calloc function. I
consider that removing duplicate code enhances code cleanliness and
facilitates maintainability.

src/mpool.c

@@ -120,12 +120,7 @@ void *mpool_alloc(mpool_t *mp)
 
 void *mpool_calloc(mpool_t *mp)
 {
-    if (!mp->chunk_count && !(mpool_extend(mp)))
-        return NULL;
-
-    char *ptr = (char *) mp->free_chunk_head + sizeof(memchunk_t);
-    mp->free_chunk_head = mp->free_chunk_head->next;
-    mp->chunk_count--;
+    char *ptr = mpool_alloc(mp);
     memset(ptr, 0, mp->chunk_size);
     return ptr;
 }