autoTickRound: use default minexponent if undefined

Author: imartinezvazquez

src/plots/cartesian/axes.js

@@ -1042,7 +1042,8 @@ function autoTickRound(ax) {
 
         var maxend = Math.max(Math.abs(rng[0]), Math.abs(rng[1]));
         var rangeexp = Math.floor(Math.log(maxend) / Math.LN10 + 0.01);
-        if(Math.abs(rangeexp) > ax.minexponent) {
+        var minexponent = ax.minexponent === undefined ? 3 : ax.minexponent;
+        if(Math.abs(rangeexp) > minexponent) {
             if(isSIFormat(ax.exponentformat) && !beyondSI(rangeexp)) {
                 ax._tickexponent = 3 * Math.round((rangeexp - 1) / 3);
             } else ax._tickexponent = rangeexp;