fix: setViewport can cause a crash if voi or scale are not provided (#493)

* be safer when merging options in setViewport

* added a test

* Update comment in test

* remove yarn.lock so travis can run

Author: mikehazell

src/setViewport.js

@@ -35,12 +35,12 @@ export default function (element, viewport) {
   // Prevent window width from being too small (note that values close to zero are valid and can occur with
   // PET images in particular)
   if (enabledElement.viewport.voi.windowWidth) {
-    enabledElement.viewport.voi.windowWidth = Math.max(viewport.voi.windowWidth, MIN_WINDOW_WIDTH);
+    enabledElement.viewport.voi.windowWidth = Math.max(enabledElement.viewport.voi.windowWidth, MIN_WINDOW_WIDTH);
   }
 
   // Prevent scale from getting too small
   if (enabledElement.viewport.scale) {
-    enabledElement.viewport.scale = Math.max(viewport.scale, MIN_VIEWPORT_SCALE);
+    enabledElement.viewport.scale = Math.max(enabledElement.viewport.scale, MIN_VIEWPORT_SCALE);
   }
 
   // Normalize the rotation value to a positive rotation in degrees

test/setViewport_test.js

@@ -93,6 +93,28 @@ describe('Set an enabled element\'s viewport', function () {
     });
   });
 
+  it('all properties should be optional', function () {
+
+    // Act
+    displayImage(this.element, this.image, this.viewport);
+
+    const element = this.element;
+    const initialViewport = getViewport(element);
+
+    const newViewport = {};
+
+    // Act
+    setViewport(element, newViewport);
+
+    // Assert
+    const viewport = getViewport(element);
+
+    // We expect all the properties to be the same but we're really testing that the method did
+    // not throw by unintentionally relying on a property existing on the input.
+    assert.deepEqual(initialViewport, viewport);
+
+  });
+
   it('should prevent windowWidth from getting too small', function () {
 
     // Act