Fix issue with insertion of whitespace when the package is disabled.

Issue reported by Brent Longborough.

todonotes.dtx

@@ -1523,7 +1523,7 @@
 % First is the current location in the document stored, this enables
 % us later to connect this point with the inserted todonote. 
 %    \begin{macrocode}
-\begin{tikzpicture}[remember picture, baseline=-0.75ex]%
+\begin{tikzpicture}[remember picture, overlay, baseline=-0.75ex]%
     \node [coordinate] (inText) {};%
 \end{tikzpicture}%
 \marginpar[{% Draw note in left margin