wayland: Better handle event times that cross zero

Detect times that cross forward/backward across the zero timepoint, and handle them appropriately, so that events with an old timestamp don't mangle the time base offset, or have their timestamps mangled.

src/video/wayland/SDL_waylandevents.c

@@ -215,16 +215,32 @@ static Uint64 Wayland_AdjustEventTimestampBase(Uint64 nsTimestamp)
  */
 static Uint64 Wayland_EventTimestampMSToNS(Uint32 wl_timestamp_ms)
 {
+    static const Uint32 ROLLOVER_INTERVAL_LOW = SDL_MAX_UINT32 / 16;
+    static const Uint32 ROLLOVER_INTERVAL_HIGH = ROLLOVER_INTERVAL_LOW * 15;
+
     static Uint64 timestamp_offset = 0;
     static Uint32 last = 0;
+    Uint64 timestamp = SDL_MS_TO_NS(wl_timestamp_ms) + timestamp_offset;
 
-    // Handle 32-bit timer rollover.
-    if (wl_timestamp_ms < last) {
-        timestamp_offset += SDL_MS_TO_NS(SDL_UINT64_C(0x100000000));
+    if (wl_timestamp_ms >= last) {
+        if (timestamp_offset && last < ROLLOVER_INTERVAL_LOW && wl_timestamp_ms > ROLLOVER_INTERVAL_HIGH) {
+            // A time that crossed backwards across zero was received. Subtract the increased time base offset.
+            timestamp -= SDL_MS_TO_NS(SDL_UINT64_C(0x100000000));
+        } else {
+            last = wl_timestamp_ms;
+        }
+    } else {
+        /* Only increment the base time offset if the timer actually crossed forward across 0,
+         * and not if this is just a timestamp from a slightly older event.
+         */
+        if (wl_timestamp_ms < ROLLOVER_INTERVAL_LOW && last > ROLLOVER_INTERVAL_HIGH) {
+            timestamp_offset += SDL_MS_TO_NS(SDL_UINT64_C(0x100000000));
+            timestamp += SDL_MS_TO_NS(SDL_UINT64_C(0x100000000));
+            last = wl_timestamp_ms;
+        }
     }
-    last = wl_timestamp_ms;
 
-    return SDL_MS_TO_NS(wl_timestamp_ms) + timestamp_offset;
+    return timestamp;
 }
 
 /* Even if high-res timestamps are available, the millisecond timestamps are still processed