Remove extra thumbnail isNull check

In case the cached thumbnail loaded successfully the isNull check is
unreachable due to the early `return true`.

thumbnail/thumbnail.cpp

@@ -676,29 +676,26 @@ bool ThumbnailProtocol::createSubThumbnail(QImage& thumbnail, const QString& fil
             }
         }
 
-        if (thumbnail.isNull()) {
-            // no cached version is available, a new thumbnail must be created
-
-            ThumbCreator* subCreator = getSubCreator();
-            if (subCreator && subCreator->create(filePath, cacheSize, cacheSize, thumbnail)) {
-                scaleDownImage(thumbnail, cacheSize, cacheSize);
-
-                // The thumbnail has been created successfully. Store the thumbnail
-                // to the cache for future access.
-                QSaveFile thumbnailfile(thumbPath.absoluteFilePath(thumbName));
-                if (thumbnailfile.open(QIODevice::WriteOnly | QIODevice::Truncate)) {
-                    QFileInfo fi(filePath);
-                    thumbnail.setText(QStringLiteral("Thumb::URI"), QString::fromUtf8(fileUrl));
-                    thumbnail.setText(QStringLiteral("Thumb::MTime"), QString::number(fi.lastModified().toSecsSinceEpoch()));
-                    thumbnail.setText(QStringLiteral("Thumb::Size"), QString::number(fi.size()));
-
-                    if (thumbnail.save(&thumbnailfile, "png")) {
-                        thumbnailfile.commit();
-                    }
+        // no cached version is available, a new thumbnail must be created
+        ThumbCreator* subCreator = getSubCreator();
+        if (subCreator && subCreator->create(filePath, cacheSize, cacheSize, thumbnail)) {
+            scaleDownImage(thumbnail, cacheSize, cacheSize);
+
+            // The thumbnail has been created successfully. Store the thumbnail
+            // to the cache for future access.
+            QSaveFile thumbnailfile(thumbPath.absoluteFilePath(thumbName));
+            if (thumbnailfile.open(QIODevice::WriteOnly | QIODevice::Truncate)) {
+                QFileInfo fi(filePath);
+                thumbnail.setText(QStringLiteral("Thumb::URI"), QString::fromUtf8(fileUrl));
+                thumbnail.setText(QStringLiteral("Thumb::MTime"), QString::number(fi.lastModified().toSecsSinceEpoch()));
+                thumbnail.setText(QStringLiteral("Thumb::Size"), QString::number(fi.size()));
+
+                if (thumbnail.save(&thumbnailfile, "png")) {
+                    thumbnailfile.commit();
                 }
-            } else {
-                return false;
             }
+        } else {
+            return false;
         }
     } else {
         ThumbCreator* subCreator = getSubCreator();