ftl: fix order of preliminary checks

source/ftl/ftl.c

@@ -25,6 +25,11 @@ size_t ftl_read(struct ftl_map *map, void *data, size_t len, uint32_t va)
 	int ret;
 	uint32_t mask, offset, page;
 
+	if (!data)
+		return 0;
+
+	len = min(len, (1 << map->log2_page_size) - offset);
+
 	mask = ((1 << map->log2_page_size) - 1);
 	offset = va & mask;
 	va >>= map->log2_page_size;
@@ -34,11 +39,6 @@ size_t ftl_read(struct ftl_map *map, void *data, size_t len, uint32_t va)
 		return len;
 	}
 
-	if (!data)
-		return 0;
-
-	len = min(len, (1 << map->log2_page_size) - offset);
-
 	return flash_read(map->dev, (page << map->log2_page_size) + offset, data,
 		len);
 }