Do not show empty parenthesis on log entry with no block flags

When nothing is stored in the database, the explode in
LogPage::formatBlockFlags will explode a empty string to a array with a
empty string as only value. Changed the count(array) check to empty
string check.

Bug: 47035
Change-Id: I879169599a2a24b35e26d4a23ab8202f267d8b00
Merge "Do not show empty parenthesis on log entry with no block flags"