Empty array casting fix (#457)

* Empty array casting fix

Signed-off-by: Alex Black <blacka101@gmail.com>

* Tests

Signed-off-by: Alex Black <blacka101@gmail.com>

nd4j/nd4j-backends/nd4j-api-parent/nd4j-api/src/main/java/org/nd4j/linalg/api/ndarray/BaseNDArray.java

@@ -5521,7 +5521,7 @@ public abstract class BaseNDArray implements INDArray, Iterable {
     public INDArray castTo(DataType dataType) {
         if(dataType == dataType())  //No-op if correct datatype
             return this;
-        if(isEmpty()){
+        if(isEmpty() && rank() == 0){
             return Nd4j.empty(dataType);
         }
         val result = Nd4j.createUninitialized(dataType, this.shape(), this.ordering());

nd4j/nd4j-backends/nd4j-tests/src/test/java/org/nd4j/linalg/Nd4jTestsC.java

@@ -8414,6 +8414,26 @@ public class Nd4jTestsC extends BaseNd4jTest {
         }
     }
 
+
+    @Test
+    public void testShape0Casts(){
+        for(DataType dt : DataType.values()){
+            if(!dt.isNumerical())
+                continue;
+
+            INDArray a1 = Nd4j.create(dt, 1,0,2);
+
+            for(DataType dt2 : DataType.values()){
+                if(!dt2.isNumerical())
+                    continue;
+                INDArray a2 = a1.castTo(dt2);
+
+                assertArrayEquals(a1.shape(), a2.shape());
+                assertEquals(dt2, a2.dataType());
+            }
+        }
+    }
+
     @Override
     public char ordering() {
         return 'c';