feat: handle maxscale default in scaleExtent

Author: mojoaxel

src/components/modebar/buttons.js

@@ -551,7 +551,7 @@ function handleGeo(gd, ev) {
             var minscale = geoLayout.projection.minscale;
             var maxscale = geoLayout.projection.maxscale;
 
-            if(maxscale < 0) maxscale = Infinity;
+            if(maxscale === -1) maxscale = Infinity;
             var newScale = (val === 'in') ? 2 * scale : 0.5 * scale;
 
             // make sure the scale is within the min/max bounds

src/plots/geo/geo.js

@@ -749,9 +749,10 @@ function getProjection(geoLayout) {
 
 	// https://github.com/d3/d3-zoom/blob/master/README.md#zoom_scaleExtent
 	projection.scaleExtent = function () {
-		var minscale = projLayout.minscale * 100;
-		var maxscale = projLayout.maxscale * 100;
-		return [minscale, maxscale];
+		var minscale = projLayout.minscale;
+		var maxscale = projLayout.maxscale;
+		if (maxscale === -1) maxscale = Infinity;
+		return [100 * minscale, 100 * maxscale];
 	};
 
 	if (geoLayout._isSatellite) {