in_windows_eventlog2: remove unexpected spaces in parsing description

[Watson1978]

Fix https://github.com/fluent/fluent-plugin-windows-eventlog/issues/116

Previously, the parser assumed that field keys and values were always separated by tab characters ("\t" or "\t\t").

However, some event log entries may include the spaces as delimiters, it causes incorrect key-value splitting.

This patch updates the parser to correctly handle both tabs and spaces between fields.