fix io exception in RNFetchBlobReq

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

                 }
 
                 RNFetchBlobFileResp rnFetchBlobFileResp;
-                
+
                 try {
                     rnFetchBlobFileResp = (RNFetchBlobFileResp) responseBody;
                 } catch (ClassCastException ex) {
                     // unexpected response type
                     if (responseBody != null) {
-                        callback.invoke("Unexpected FileStorage response file: " + responseBody.body().string(), null);
+                        String responseBodyString = null;
+                        try {
+                            responseBodyString = responseBody.string();
+                        } catch(IOException exception) {
+                            exception.printStackTrace();
+                        }
+                        callback.invoke("Unexpected FileStorage response file: " + responseBodyString, null);
                     } else {
                         callback.invoke("Unexpected FileStorage response with no file.", null);
                     }