added small optimization to FSStorage.readBlock to read blocks from i…

…n-memory buffer if possible

lib/fs_storage.js

@@ -88,6 +88,12 @@ FSStorage.prototype.readBlock = function (index, offset, length, cb) {
   var piece = self.pieces[index]
   if (!piece) return cb(new Error("invalid piece index " + index))
 
+  if (piece.verified && piece.buffer) {
+    // piece is verified and cached in memory, so read directly from its buffer
+    // instead of reading from the filesystem.
+    return piece.readBlock(offset, length, cb)
+  }
+
   var rangeFrom = offset
   var rangeTo = rangeFrom + length