display: partially inline vout_display_GetDefaultDisplaySize()

Only from vout_display_New() can (and should) the window size be used
rather than the ideal default display size. In the other call sites,
we actually want to compute the ideal size regardless of the actual
window size.

Take that case out of vout_display_GetDefaultDisplaySize() to enable
further refactoring. This is a non-functional change, except for the
added run-time warning.

src/video_output/display.c

@@ -76,15 +76,8 @@ void vout_display_GetDefaultDisplaySize(unsigned *width, unsigned *height,
                                         const vout_display_cfg_t *cfg)
 {
     bool from_source = true;
-    /* Size reported by the window module */
-    if (cfg->window_props.width != 0 && cfg->window_props.height != 0) {
-        *width = cfg->window_props.width;
-        *height = cfg->window_props.height;
-        /* The dimensions are not initialized from the source format */
-        from_source = false;
-    }
     /* Use the original video size */
-    else if (source->i_sar_num >= source->i_sar_den) {
+    if (source->i_sar_num >= source->i_sar_den) {
         *width  = (int64_t)source->i_visible_width * source->i_sar_num * cfg->display.sar.den / source->i_sar_den / cfg->display.sar.num;
         *height = source->i_visible_height;
     } else {
@@ -660,8 +653,16 @@ vout_display_t *vout_display_New(vlc_object_t *parent,
         return NULL;
 
     unsigned display_width, display_height;
-    vout_display_GetDefaultDisplaySize(&display_width, &display_height,
-                                       source, cfg);
+
+    if (cfg->window_props.width == 0 || cfg->window_props.height == 0) {
+        /* Work around buggy window provider */
+        msg_Warn(parent, "window size missing");
+        vout_display_GetDefaultDisplaySize(&display_width, &display_height,
+                                           source, cfg);
+    } else {
+        display_width = cfg->window_props.width;
+        display_height = cfg->window_props.height;
+    }
 
     osys->cfg = *cfg;
     /* The window size was used for the initial setup. Now it can be dropped in