Merge pull request #423 from ankit-makwana/hash-fix

Fix #170 - RNFetchBlob fs hash with md5 param fails if the file size is 0(blank file)

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

             int chunkSize = 4096 * 256; // 1Mb
             byte[] buffer = new byte[chunkSize];
 
-            int bytesRead;
-            while ((bytesRead = inputStream.read(buffer)) != -1) {
-                md.update(buffer, 0, bytesRead);
+            if(file.length() != 0) {
+                int bytesRead;
+                while ((bytesRead = inputStream.read(buffer)) != -1) {
+                    md.update(buffer, 0, bytesRead);
+                }
             }
 
             StringBuilder hexString = new StringBuilder();