Handle log file list timeout with prettier error message

Above is the error message that appears if a flight controller doesn't have an SD card inserted and the user pushes the "Download DataFlash Log Via Mavlink" button.

I think we could make this prettier, perhaps just shorten it to "Timeout while attempting to download list of logfiles" or something similar.

No source file, entry point, or test is named in the issue. Locate the handler for the “Download DataFlash Log Via Mavlink” button and reproduce the missing-SD-card timeout, then verify that the displayed error is shortened to a clear message such as the one proposed.

Written by the indexing model from the issue text.