SDL: Clarify that timeout == 0 is handled at the top of SDL_WaitEventTimeout()

From 2592e6219b644035eb68d466f5e044f42627873a Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Thu, 6 Jan 2022 13:30:26 -0800
Subject: [PATCH] Clarify that timeout == 0 is handled at the top of
 SDL_WaitEventTimeout()

---
 src/events/SDL_events.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/events/SDL_events.c b/src/events/SDL_events.c
index 65415d0f355..f5ead49a3b7 100644
--- a/src/events/SDL_events.c
+++ b/src/events/SDL_events.c
@@ -974,8 +974,7 @@ SDL_WaitEventTimeout(SDL_Event * event, int timeout)
 {
     SDL_VideoDevice *_this = SDL_GetVideoDevice();
     SDL_Window *wakeup_window;
-    Uint32 start = 0;
-    Uint32 expiration = 0;
+    Uint32 start, expiration;
     SDL_bool include_sentinel = (timeout == 0) ? SDL_TRUE : SDL_FALSE;
 
     /* If there isn't a poll sentinel event pending, pump events and add one */
@@ -1006,10 +1005,15 @@ SDL_WaitEventTimeout(SDL_Event * event, int timeout)
         /* Has existing events */
         return 1;
     }
+    /* We should have completely handled timeout == 0 above */
+    SDL_assert(timeout != 0);
 
     if (timeout > 0) {
         start = SDL_GetTicks();
         expiration = start + timeout;
+    } else {
+        start = 0;
+        expiration = 0;
     }
 
     if (_this && _this->WaitEventTimeout && _this->SendWakeupEvent && !SDL_events_need_polling()) {