Raise warnings if there is no system in the path listed in sys_configs (#1130)

If the user writes a wrong path in "sys_configs", this warning can help
locate the problem.

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: HuangJiameng

dpgen/generator/run.py

@@ -1004,7 +1004,13 @@ def make_model_devi(iter_index, jdata, mdata):
         cur_systems = []
         ss = sys_configs[idx]
         for ii in ss:
-            cur_systems += sorted(glob.glob(ii))
+            ii_systems = sorted(glob.glob(ii))
+            if ii_systems == []:
+                warnings.warn(
+                    "There is no system in the path %s. Please check if the path is correct."
+                    % ii
+                )
+            cur_systems += ii_systems
         # cur_systems should not be sorted, as we may add specific constrict to the similutions
         # cur_systems.sort()
         cur_systems = [os.path.abspath(ii) for ii in cur_systems]