Fix a 404, add some further code consistency

[stevekay]

Some fairly trivial and non-functional changes here, but figured worth addressing.

• rrd link was wrong, gave 404, revised to point at its new location
• replaced text mid-night with midnight, consistent with remainder of repo
• code style, inserted a missing space after if, consistent with remainder of repo
• code style, inserted a blank line after while, consistent with remainder of repo

[sysstat]

Thanks for those changes.
Wrt to the blank line after while, I must admit that I don't have strict rules here. I will apply the corresponding commit anyway.
Thanks again.