[bsp][wch]修复scons --dist (#10473)

fix wch scons --dist

bsp/wch/risc-v/tools/sdk_dist.py

@@ -14,8 +14,9 @@ def dist_do_building(BSP_ROOT, dist_dir):
     print("=> copy ch32 bsp library")
     library_dir = os.path.join(dist_dir, 'Libraries')
     library_path = os.path.join(os.path.dirname(BSP_ROOT), 'Libraries')
-    bsp_copy_files(os.path.join(library_path, rtconfig.BSP_LIBRARY_TYPE), os.path.join(library_dir, rtconfig.BSP_LIBRARY_TYPE))
-
+    if rtconfig.BSP_LIBRARY_TYPE is not None:
+        bsp_copy_files(os.path.join(library_path, rtconfig.BSP_LIBRARY_TYPE),
+                    os.path.join(library_dir, rtconfig.BSP_LIBRARY_TYPE))
     print("=> copy bsp drivers")
     bsp_copy_files(os.path.join(library_path, 'ch32_drivers'), os.path.join(library_dir, 'ch32_drivers'))
     shutil.copyfile(os.path.join(library_path, 'Kconfig'), os.path.join(library_dir, 'Kconfig'))