Fix incorrect UTF-8 data conversion issue when the data contains special characters.

Author: wkh237

android/src/main/java/com/RNFetchBlob/RNFetchBlobFS.java

@@ -250,10 +250,7 @@ public void readStream(String path, String encoding, int bufferSize, int tick, f
                 CharsetEncoder encoder = Charset.forName("UTF-8").newEncoder();
                 while ((cursor = fs.read(buffer)) != -1) {
                     encoder.encode(ByteBuffer.wrap(buffer).asCharBuffer());
-                    String chunk = new String(buffer);
-                    if(cursor != bufferSize) {
-                        chunk = chunk.substring(0, cursor);
-                    }
+                    String chunk = new String(buffer, 0, cursor);
                     emitStreamEvent(streamId, "data", chunk);
                     if(tick > 0)
                         SystemClock.sleep(tick);