fix: page crash when dots is true and step is null (#838)

* fix: page crash when dots is true and step is null

* test: add test case

* test: update test case

Author: denghuacc

src/Steps/index.tsx

@@ -24,7 +24,7 @@ export default function Steps(props: StepsProps) {
     });
 
     // Fill dots
-    if (dots) {
+    if (dots && step !== null) {
       let current = min;
       while (current <= max) {
         dotSet.add(current);

tests/common.test.js

@@ -51,6 +51,11 @@ describe('Common', () => {
     expect(container2.getElementsByClassName('rc-slider-dot-active')).toHaveLength(4);
   });
 
+  it('should render normally when `dots=true` and `step=null`', () => {
+    const { container } = render(<Slider step={null} dots />);
+    expect(() => container).not.toThrowError();
+  });
+
   it('should render dots correctly when dotStyle is dynamic`', () => {
     const { container: container1 } = render(
       <Slider value={50} step={10} dots dotStyle={(dotValue) => ({ width: `${dotValue}px` })} />,