LOG Download does not rename last downloaded LOG

Hi,

The Log-Download via Serial Link (Using the Button) did rename every downloaded Logfile to the date and time it was produced except the last one.
The last one got the time and date of download and the LOG Number minus one.
I used "Download All Logs".

In my Case there were 3 LOGs to download.

Arducopter. 3.1.4 on APM 2.5
Mission Planner 1.3.2 build 1.1.5255.13235

Start with the Log-Download via Serial Link flow used by the “Download All Logs” button and reproduce the case with three logs on the stated Mission Planner and ArduCopter versions. Trace how each downloaded LOG is named; done means the final log uses its production date and time and the correct LOG number rather than the download time and number minus one.

Written by the indexing model from the issue text.