Fix downloads not working for custom SD card paths (closes #3564)

(cherry picked from commit ad9f646102caf2079c6939fabdef7ccf292c0e52)

app/src/main/java/eu/kanade/tachiyomi/util/storage/DiskUtil.kt

@@ -34,11 +34,14 @@ object DiskUtil {
      * Gets the available space for the disk that a file path points to, in bytes.
      */
     fun getAvailableStorageSpace(f: UniFile): Long {
-        val stat = StatFs(f.filePath)
-        val availBlocks = stat.availableBlocksLong
-        val blockSize = stat.blockSizeLong
+        val stat = try {
+            StatFs(f.filePath)
+        } catch (_: Exception) {
+            // Assume that exception is thrown when path is on external storage
+            StatFs(Environment.getExternalStorageDirectory().path)
+        }
 
-        return availBlocks * blockSize
+        return stat.availableBlocksLong * stat.blockSizeLong
     }
 
     /**