[gimp] plug-ins: fix some warnings in Win32 screenshot code.

[Jehan <jehanp src gnome org>]

commit 70cf57154f729e08a503ec99b858386296267fdf
Author: Jehan <jehan girinstud io>
Date:   Sun Aug 2 19:49:22 2020 +0200

    plug-ins: fix some warnings in Win32 screenshot code.
    
    Fixes:
    > warning: old-style function definition [-Wold-style-definition]

 plug-ins/screenshot/screenshot-win32-magnification-api.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/plug-ins/screenshot/screenshot-win32-magnification-api.h 
b/plug-ins/screenshot/screenshot-win32-magnification-api.h
index ff3a82495d..a204c80b21 100644
--- a/plug-ins/screenshot/screenshot-win32-magnification-api.h
+++ b/plug-ins/screenshot/screenshot-win32-magnification-api.h
@@ -100,7 +100,7 @@ void UnLoadMagnificationLibrary(void);
 BOOL LoadMagnificationLibrary(void);
 
 
-void UnLoadMagnificationLibrary()
+void UnLoadMagnificationLibrary(void)
 {
   if (!magnificationLibrary) return;
   FreeLibrary(magnificationLibrary);
@@ -108,7 +108,7 @@ void UnLoadMagnificationLibrary()
 
 
 
-BOOL LoadMagnificationLibrary()
+BOOL LoadMagnificationLibrary(void)
 {
   if (magnificationLibrary) return TRUE;