use _needsExpand to determine if new rangeslider range is required

- instead of `(!rangeslider.range)`-based criterion
- which allows for data update to correctly expand the range slider
- rm now useless axis.autorange criterion for _needsExpand

Author: etpinard

src/components/rangeslider/defaults.js

@@ -36,7 +36,7 @@ module.exports = function handleDefaults(layoutIn, layoutOut, axName) {
     coerce('range');
 
     // Expand slider range to the axis range
-    if(containerOut.range && !axOut.autorange) {
+    if(containerOut.range) {
         // TODO: what if the ranges are reversed?
         var outRange = containerOut.range,
             axRange = axOut.range;

src/components/rangeslider/draw.js

@@ -82,7 +82,7 @@ module.exports = function(gd) {
         // compute new slider range using axis autorange if necessary
         // copy back range to input range slider container to skip
         // this step in subsequent draw calls
-        if(!opts.range) {
+        if(axisOpts._needsExpand && axisOpts._min.length && axisOpts._max.length) {
             opts._input.range = opts.range = Axes.getAutoRange(axisOpts);
         }