Temporary style builders: Do nothing if content lambda does not emit commands

[okarmazin]

There is no reason to apply and immediately revert a style if there was no content to be affected by the style.

The following pattern currently blindly emits the surrounding Command.TextSize(2,2), Command.TextSize(1,1).

// current text size: 1x1
withTextSize(2, 2) {
  // This does nothing, so why not avoid 
  // setting the temporary 2x2 text size as well?
}

While emitting the commands is benign, it would be nice if we didn't send unnecessary commands to the printer.

Task: If the content lambda of temporary style builders didn't do anything, do not apply the surrounding style either.