prevent returning dirty buffer in readStream

Fixes RonRadtke#180

Author: tszheichoi

android/src/main/java/com/ReactNativeBlobUtil/ReactNativeBlobUtilStream.java

@@ -69,16 +69,20 @@ else if (resolved == null) {
             int cursor = 0;
             boolean error = false;
 
+            
+
             if (encoding.equalsIgnoreCase("utf8")) {
                 InputStreamReader isr = new InputStreamReader(fs, Charset.forName("UTF-8"));
                 BufferedReader reader = new BufferedReader(isr, chunkSize);
                 char[] buffer = new char[chunkSize];
                 // read chunks of the string
-                while (reader.read(buffer, 0, chunkSize) != -1) {
-                    String chunk = new String(buffer);
+                int numBytesRead = reader.read(buffer, 0, chunkSize);
+                while (numBytesRead != -1) {
+                    String chunk = new String(buffer, 0, numBytesRead);
                     emitStreamEvent(streamId, "data", chunk);
                     if (tick > 0)
                         SystemClock.sleep(tick);
+                    numBytesRead = reader.read(buffer, 0, chunkSize);
                 }
 
                 reader.close();