sdl12-compat: The SDL2 "dummy" video driver reports a vidmode of 0x0, so don't assert on it.

From 6b2d3dfcdc49da5d46666eedfe1f01251c23acf4 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Thu, 17 Jun 2021 10:57:07 -0400
Subject: [PATCH] The SDL2 "dummy" video driver reports a vidmode of 0x0, so
 don't assert on it.

---
 src/SDL12_compat.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
index f8c6f10..224a87b 100644
--- a/src/SDL12_compat.c
+++ b/src/SDL12_compat.c
@@ -1517,10 +1517,11 @@ Init12VidModes(void)
         if (SDL20_GetDisplayMode(VideoDisplayIndex, i, &mode) < 0) {
             continue;
         }
-        if (!mode.w || !mode.h) {
-            SDL_assert(0 && "Can this actually happen?");
+
+        if ((mode.w <= 0) || (mode.h <= 0)) {
             continue;
         }
+
         if (mode.w > 65535 || mode.h > 65535) {
             continue;  /* can't fit to 16-bits for SDL12_Rect */
         }