Fixing TF_String for jpeg_encode

src/TensorFlowNET.Core/Sessions/BaseSession.cs

@@ -278,8 +278,8 @@ namespace Tensorflow
                             ret = NDArray.Scalar(*(bool*) srcAddress);
                             break;
                         case TF_DataType.TF_STRING:
-                            using (var reader = new CodedInputStream(new IntPtr(srcAddress).Stream(8, (long) tensor.bytesize)))
-                                ret = NDArray.FromString(reader.ReadString());
+                            using (var reader = new CodedInputStream(new IntPtr(srcAddress).Stream(8, (long)tensor.bytesize)))
+                                ret = new NDArray(reader.ReadBytes().ToByteArray());
                             break;
                         case TF_DataType.TF_UINT8:
                             ret = NDArray.Scalar(*(byte*) srcAddress);

test/TensorFlowNET.UnitTest/SessionTest.cs

@@ -109,7 +109,7 @@ namespace TensorFlowNET.UnitTest
                 var c = tf.strings.substr(a, 4, 8);
                 using (var sess = tf.Session())
                 {
-                    var result = (string) c.eval(sess);
+                    var result = System.Text.UTF8Encoding.UTF8.GetString((byte[]) c.eval(sess));
                     Console.WriteLine(result);
                     result.Should().Be("heythere");
                 }
@@ -126,7 +126,7 @@ namespace TensorFlowNET.UnitTest
                 var c = tf.strings.substr(a, 0, size - 5000);
                 using (var sess = tf.Session())
                 {
-                    var result = (string) c.eval(sess);
+                    var result = System.Text.UTF8Encoding.UTF8.GetString((byte[]) c.eval(sess));
                     Console.WriteLine((string) result);
                     result.Should().HaveLength(size - 5000).And.ContainAll("a");
                 }