Call fflush() before ftruncate() to drop all buffered data (#914)

Call fflush() before ftruncate() to drop all buffered data (#914)

This avoids stale data presented to caller via a fread()

Current bug due to the buffered data can be seen in stripping mp3s of tags

    f.strip(ID3v1);
    f.strip(APE);

The ID3v1 tag sits at the end of file (strip calls ftruncate()) and the APE
strip performs a readFile() that would return the stream buffered/truncated data
and reinsert