jscript: add missing prototype

[Austin English]

-- 
-Austin
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diff --git a/dlls/jscript/jscript.h b/dlls/jscript/jscript.h
index 533be57..4451669 100644
--- a/dlls/jscript/jscript.h
+++ b/dlls/jscript/jscript.h
@@ -369,7 +369,7 @@ static inline void num_set_nan(VARIANT *v)
 #endif
 }
 
-static inline DOUBLE ret_nan()
+static inline DOUBLE ret_nan(void)
 {
     VARIANT v;
     num_set_nan(&v);