Unbreak pkgconfig by not having the list start with a comma.

Index: configure
--- configure.orig
+++ configure
@@ -13597,7 +13597,7 @@ else
 $as_echo "yes" >&6; }
 
     HAVE_OGG="yes"
-    SHOUT_REQUIRES="$SHOUT_REQUIRES, ogg"
+    SHOUT_REQUIRES="ogg"
 
 fi
 OGG_LIBS="$OGG_LDFLAGS $OGG_LIBS"