Fix slide modal preview sizing

src/web/public/js/slides/slide-form.js

@@ -792,7 +792,12 @@ import { createSlideAnimationEditor } from '/assets/js/slides/slide-animation-ed
     var containerStyle = window.getComputedStyle(stageContainer);
     var availableWidth = stageContainer.clientWidth - parseFloat(containerStyle.paddingLeft) - parseFloat(containerStyle.paddingRight);
     var maxHeight = parseFloat(window.getComputedStyle(slidePreviewStage).maxHeight);
-    if (!availableWidth || !Number.isFinite(maxHeight)) {
+    if (!Number.isFinite(maxHeight)) {
+      slidePreviewStage.style.removeProperty('width');
+      slidePreviewStage.style.removeProperty('margin-inline');
+      return;
+    }
+    if (!availableWidth) {
       return;
     }