Fix pdfpc notes appearing one slide too early

Beamer start with slide number 0 for the title page, whereas pdfpc
starts counting from 1.

beamertheme-source/pdfpcnotes.dtx

@@ -92,7 +92,11 @@
 		\let\lastframenumber\theframenumber
 		\begingroup
 			\let\#\hashchar
-			\immediate\write\pdfpcnotesfile{\#\#\# \theframenumber}%
+			% pdfpc counts the title page as slide 1
+			% thus all note numbers are off by one
+			\newcount\pdfpcframenumber
+			\pdfpcframenumber=\numexpr\theframenumber + 1\relax
+			\immediate\write\pdfpcnotesfile{\#\#\# \the\pdfpcframenumber}%
 		\endgroup
 	\fi