Log files with invalid JSON

ltsdb_json.py

@@ -42,6 +42,9 @@ class LTS:
                 fcntl.flock(fh, fcntl.LOCK_EX)
                 json.dump({"description": self.description, "data": self.data}, fh)
             self.rebuild_index()
+        except json.decoder.JSONDecodeError as e:
+            log.exception(f"Cannot decode JSON in {self.filename}: {e}")
+            raise
 
     def pop(self, i):
         # Pop the element at index i and adjust the min/max values of the