Style: Fixup instances of void arguments

The style we have here is that functions with no arguments are to have
explicit `void` arguments, even though this doesn't apply in C++,
because it does apply in C.

Unfortunately, some have slipped through the cracks. This commit fixes
them.

desktop_version/src/Music.h

@@ -19,7 +19,7 @@ public:
     void destroy(void);
 
     void play(int t);
-    void resume();
+    void resume(void);
     void resumefade(const int fadein_ms);
     void pause(void);
     void haltdasmusik(void);