修复主窗口启动时相册集封面不显示问题

- 裁剪封面是本地文件，直接使用Uri.fromFile加载
- 文件不存在时使用MediaStore查询

gallery/src/main/java/cc/winboll/studio/gallery/MainActivity.java

@@ -194,7 +194,12 @@ private void loadAlbums() {
                 String coverPath = coverDbHelper.getCover(albumPath);
                 Uri coverUri = null;
                 if (coverPath != null) {
-                    coverUri = getUriFromPath(coverPath);
+                    File coverFile = new File(coverPath);
+                    if (coverFile.exists()) {
+                        coverUri = Uri.fromFile(coverFile);
+                    } else {
+                        coverUri = getUriFromPath(coverPath);
+                    }
                 }
                 if (coverUri == null) {
                     ArrayList<Uri> images = getImagesInFolder(albumPath);