add fallback to annotations/images convertCoords

- so that they don't throw exceptions with the
  excepted axis container is undefined.

Author: etpinard

src/components/annotations/convert_coords.js

@@ -26,6 +26,8 @@ var toLogRange = require('../../lib/to_log_range');
  *     same relayout call should override this conversion.
  */
 module.exports = function convertCoords(gd, ax, newType, doExtra) {
+    ax = ax || {};
+
     var toLog = (newType === 'log') && (ax.type === 'linear'),
         fromLog = (newType === 'linear') && (ax.type === 'log');
 

src/components/images/convert_coords.js

@@ -31,6 +31,8 @@ var toLogRange = require('../../lib/to_log_range');
  *     same relayout call should override this conversion.
  */
 module.exports = function convertCoords(gd, ax, newType, doExtra) {
+    ax = ax || {};
+
     var toLog = (newType === 'log') && (ax.type === 'linear'),
         fromLog = (newType === 'linear') && (ax.type === 'log');
 

test/jasmine/tests/gl_plot_interact_test.js

@@ -679,6 +679,23 @@ describe('Test gl3d relayout calls', function() {
         .then(done);
     });
 
+    it('should skip root-level axis objects', function(done) {
+        Plotly.newPlot(gd, [{
+            type: 'scatter3d',
+            x: [1, 2, 3],
+            y: [1, 2, 3],
+            z: [1, 2, 1]
+        }])
+        .then(function() {
+            return Plotly.relayout(gd, {
+                xaxis: {},
+                yaxis: {},
+                zaxis: {}
+            });
+        })
+        .catch(fail)
+        .then(done);
+    });
 });
 
 describe('Test gl2d plots', function() {

test/jasmine/tests/plot_api_test.js

@@ -237,6 +237,21 @@ describe('Test plot api', function() {
                 })
                 .then(done);
         });
+
+        it('should skip empty axis objects', function(done) {
+            Plotly.plot(gd, [{
+                x: [1, 2, 3],
+                y: [1, 2, 1]
+            }], {
+                xaxis: { title: 'x title' },
+                yaxis: { title: 'y title' }
+            })
+            .then(function() {
+                return Plotly.relayout(gd, { zaxis: {} });
+            })
+            .catch(fail)
+            .then(done);
+        });
     });
 
     describe('Plotly.restyle', function() {