Fix empty field handling

To reproduce the bug fixed by this commit, call
logMessage("CHANNEL", "", "", "");

Expected output when splitting the string (passed into the logMessage method in the logger) into the fields:
numFields: 4
field[0]: Timestamp
field[1]: ""
field[2]: ""
field[3]: ""

But the resulting output was:
numFields: 3
field[0]: Timestamp
field[1]: ""
field[2]: "\t"
Merge pull request #24 from dohse/fix-empty-field-handling

Fix empty field handling