Use asserts in array

codegen/array/snippets/append_capped

@@ -1,6 +1,4 @@
-  if (!array || array->count >= array->capacity) {{
-    return;
-  }}
+  assert(array != NULL && array->count < array->capacity);
 
   u64 index = (array->count)++;
   wapp_{Tlower}_array_set(array, index, item);