win32: set window_corners to default for fullscreen

I don't think in fullscreen mode it makes sense to enable rounded corners.
We can add another option if someone needs it, but for now `window_corners`
affects only the window as one would expect.

video/out/w32_common.c

@@ -1043,13 +1043,23 @@ static void update_window_state(struct vo_w32_state *w32)
     signal_events(w32, VO_EVENT_RESIZE);
 }
 
+static void update_corners_pref(const struct vo_w32_state *w32) {
+    if (w32->parent)
+        return;
+
+    int pref = w32->current_fs ? 0 : w32->opts->window_corners;
+    DwmSetWindowAttribute(w32->window, DWMWA_WINDOW_CORNER_PREFERENCE,
+                          &pref, sizeof(pref));
+}
+
 static void reinit_window_state(struct vo_w32_state *w32)
 {
     if (w32->parent)
         return;
 
     // The order matters: fs state should be updated prior to changing styles
     update_fullscreen_state(w32);
+    update_corners_pref(w32);
     update_window_style(w32);
 
     // fit_on_screen is applied at most once when/if applicable (normal win).
@@ -1092,12 +1102,6 @@ static void update_dark_mode(const struct vo_w32_state *w32)
                           &use_dark_mode, sizeof(use_dark_mode));
 }
 
-static void update_corners_pref(const struct vo_w32_state *w32) {
-    DwmSetWindowAttribute(w32->window, DWMWA_WINDOW_CORNER_PREFERENCE,
-                          &w32->opts->window_corners,
-                          sizeof(w32->opts->window_corners));
-}
-
 static LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam,
                                 LPARAM lParam)
 {