Fixed A Bug.

This is a bug fix for 4063. "Notice: Array to string conversion" when downloading CSV or TSV files from Visitor Log in 1.12. 

Some custom variables are in the $csv array as arrays themselves. Line 283 was trying to handle this array as a string and was throwing the error. This fix parses the array into a string prior to the string formatting step. The csv will successfully download with this fix. Tested on PHP 5.4.13.