Fix Envelope#intersect when other is empty (#168)

Thanks!

Author: mbasmanova

src/main/java/com/esri/core/geometry/Envelope2D.java

@@ -321,8 +321,10 @@ public boolean isIntersecting(double xmin_, double ymin_, double xmax_, double y
 	 *         envelope to empty state and returns False.
 	 */
 	public boolean intersect(Envelope2D other) {
-		if (isEmpty() || other.isEmpty())
+		if (isEmpty() || other.isEmpty()) {
+			setEmpty();
 			return false;
+		}
 
 		if (other.xmin > xmin)
 			xmin = other.xmin;

src/test/java/com/esri/core/geometry/TestEnvelope.java

@@ -0,0 +1,49 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.esri.core.geometry;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class TestEnvelope
+{
+    @Test
+    public void testIntersect()
+    {
+        assertIntersection(new Envelope(0, 0, 5, 5), new Envelope(0, 0, 5, 5), new Envelope(0, 0, 5, 5));
+        assertIntersection(new Envelope(0, 0, 5, 5), new Envelope(1, 1, 6, 6), new Envelope(1, 1, 5, 5));
+        assertIntersection(new Envelope(1, 2, 3, 4), new Envelope(0, 0, 2, 3), new Envelope(1, 2, 2, 3));
+
+        assertNoIntersection(new Envelope(), new Envelope());
+        assertNoIntersection(new Envelope(0, 0, 5, 5), new Envelope());
+        assertNoIntersection(new Envelope(), new Envelope(0, 0, 5, 5));
+    }
+
+    private static void assertIntersection(Envelope envelope, Envelope other, Envelope intersection)
+    {
+        boolean intersects = envelope.intersect(other);
+        assertTrue(intersects);
+        assertEquals(envelope, intersection);
+    }
+
+    private static void assertNoIntersection(Envelope envelope, Envelope other)
+    {
+        boolean intersects = envelope.intersect(other);
+        assertFalse(intersects);
+        assertTrue(envelope.isEmpty());
+    }
+}