DFReader.py - change flag to metadata_load_attempted

Co-authored-by: Peter Barker <[email protected]>

DFReader.py

@@ -582,7 +582,7 @@ def metadata_tree(self,verbose=False):
         '''return a map between a log message and its metadata. May return None if data is not available'''
         # If we've already tried loading data, use it if we have it
         # This avoid repeated attempts, when the file is not there
-        if self.tried:
+        if self.metadata_load_attempted:
             return self.data
         self.tried = True
         # Get file name, based on vehicle type