rp2040 LittleFS flash_filer mode r+ problem

[jscrane]

There is a problem with LittleFS as used through the flash_filer on Pico: advancing through the files hangs on the second file. Also:

• The first file can be loaded OK.
• Traversing the directory with dir.next() works on its own.

This seems to be down to the use of file mode r+ (opening in mode r is fine). Also it seems to be an interaction with the PicoDVI library --- it isn't seen when not using that library.