wrlib: moved 'RShutdown' from 'load.c' to 'misc.c' for consistency

The cleanup function is actually not specific to loading images and could
do a lot more, so it is probably better placed in 'misc.c'

wrlib/misc.c

@@ -26,6 +26,8 @@
 #include <X11/Xlib.h>
 
 #include "wraster.h"
+#include "imgformat.h"
+
 
 void RBevelImage(RImage * image, int bevel_type)
 {
@@ -240,3 +242,13 @@ const char *RMessageForError(int errorCode)
 		return "internal error";
 	}
 }
+
+/*
+ * cleaning third-party libs at shutdown
+ */
+void RShutdown(void)
+{
+#ifdef USE_MAGICK
+	RReleaseMagick();
+#endif
+}