add fallback in the case of zero width or height

Author: archmoj

src/components/fx/hover.js

@@ -896,8 +896,8 @@ function createHoverText(hoverData, opts, gd) {
     var t0 = c0[axLetter + 'Label'];
     var outerContainerBB = outerContainer.node().getBoundingClientRect();
     var outerTop = outerContainerBB.top;
-    var outerWidth = outerContainerBB.width;
-    var outerHeight = outerContainerBB.height;
+    var outerWidth = outerContainerBB.width || fullLayout.width;
+    var outerHeight = outerContainerBB.height || fullLayout.height;
 
     // show the common label, if any, on the axis
     // never show a common label in array mode,