LibreVNA manual - fix rogue whitespace

Documentation/UserManual/manual.tex

@@ -1423,7 +1423,7 @@ \subsection{Creating a compound device}
 \item At least two physical devices must be used
 \item At most four physical devices can be combined with a maximum of eight virtual ports
 \end{itemize}
-\item  Assign serial numbers to each physical device. Serial numbers for all currently connected devices are available in the dropdown but it is also possible to enter a different serial number manually
+\item Assign serial numbers to each physical device. Serial numbers for all currently connected devices are available in the dropdown but it is also possible to enter a different serial number manually
 \item Assign the virtual ports of the compound device:
 \begin{itemize}
 \item Each port number must appear only once