fix: improve vertical centering of title slide

src/beamerinnerthememoloch.dtx

@@ -113,6 +113,7 @@
 \setbeamertemplate{title page}{
   \begin{minipage}[b][\paperheight]{\textwidth}
     \ifx\inserttitlegraphic\@empty\else\usebeamertemplate*{title graphic}\fi
+    \null%
     \vfill%
     \ifx\inserttitle\@empty\else\usebeamertemplate*{title}\fi
     \ifx\insertsubtitle\@empty\else\usebeamertemplate*{subtitle}\fi