Optimize generic_ping function

[fitztrev]

The generic_ping function currently sends weblog_ping() a null value if there is an empty line in the ping_sites option. The regexp pattern in the function only replaces 2 or more empty lines with 1--it doesn't get rid of it altogether. There's no check anywhere down the line to stop the IXR class from trying to ping an empty string.

This restructure will address this problem and speed the function up at the same time.

Don't ping empty strings.

(In [6853]) generic_ping() improvements from fitztrev. fixes #5855