sdl2-compat: Fixed testautomation --filter video_getNumDisplayModesNegative

SDL Commits
1 
From fb6b605be128c721c3db8b6135f1e3e8177f3faa Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Mon, 7 Aug 2023 22:53:16 -0700
Subject: [PATCH] Fixed testautomation --filter
 video_getNumDisplayModesNegative

---
 src/sdl2_compat.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/sdl2_compat.c b/src/sdl2_compat.c
index e698ce3..d3edc8f 100644
--- a/src/sdl2_compat.c
+++ b/src/sdl2_compat.c
@@ -4480,8 +4480,11 @@ SDL_GetNumDisplayModes(int displayIndex)
     int count = 0;
     const SDL_DisplayMode **list;
     list = SDL3_GetFullscreenDisplayModes(displayID, &count);
-    SDL3_free((void *)list);
-    return count;
+    if (list) {
+        SDL3_free(list);
+        return count;
+    }
+    return -1;
 }
 
 DECLSPEC int SDLCALL