Prevent reader page placeholder from getting too long in height

the "SpinnerImage" has a default height styling of 100% which caused the loading placeholder to take up all the available scroll height

src/modules/reader/utils/ReaderPager.utils.tsx

@@ -125,7 +125,12 @@ export const getImagePlaceholderStyling = (
                 }),
             };
         case ReaderPageScaleMode.ORIGINAL:
-            return defaultStyling;
+            return {
+                ...defaultStyling,
+                ...applyStyles(isContinuousVerticalReadingMode(readingMode), {
+                    height: undefined,
+                }),
+            };
         default:
             throw new Error(`Unexpected "PageScaleMode" (${pageScaleMode})`);
     }