Use asserts in array

codegen/array/snippets/extend_capped

@@ -1,11 +1,7 @@
-  if (!array || !other) {{
-    return;
-  }}
+  assert(array != NULL && other != NULL);
 
   u64 remaining_capacity = array->capacity - array->count;
-  if (other->count >= remaining_capacity) {{
-    return;
-  }}
+  assert(other->count < remaining_capacity);
 
   {T} *item;