csv: Fall back to GenericCSV for csv files with no match

If we fail to find a matching driver and the file appears to be a
".csv" file, return GenericCSV as a match. This will make us try to
open the file with the generic driver and thus capture loading error
messages and show them to the user. Otherwise we would just fail to
match a driver, and report the format is unsupported, which is
confusing to a user.

Related to #11519

chirp/directory.py

@@ -193,6 +193,12 @@ def __repr__(self):
         ex.metadata = metadata
         raise ex
     else:
+        # If we don't find anything else and the file appears to be a CSV
+        # file, then explicitly open it with the generic driver so we can
+        # get relevant errors instead of just "Unknown file format".
+        if image_file.lower().endswith('.csv'):
+            rclass = get_radio('Generic_CSV')
+            return rclass(image_file)
         raise errors.ImageDetectFailed("Unknown file format")