FIX listitem bullet without whitespace (markedjs#1980)

This makes marked render correctly with the following text:

```markdown
- item1
- item2
-Not a list item(without space)
- item3
```

Currently:
```html
<ul>
<li>item1</li>
<li>item2</li>
</ul>
<p>-Not a list item(without space)</p>
<ul>
<li>item3</li>
</ul>
```

Which should be:
```html
<ul>
<li>item1</li>
<li>item2
-Not a list item(without space)</li>
<li>item3</li>
</ul>
```

This is the rendered result for commonmark as well.

Changes:
- `nextBulletRegex` checks for whitespace after the bullet
- separately checks for hr or lheading

src/Tokenizer.js

@@ -225,18 +225,32 @@ export class Tokenizer {
         }
 
         if (!endEarly) {
-          const nextBulletRegex = new RegExp(`^ {0,${Math.min(3, indent - 1)}}(?:[*+-]|\\d{1,9}[.)])`);
+          const nextBulletRegex = new RegExp(`^ {0,${Math.min(3, indent - 1)}}(?:[*+-]|\\d{1,9}[.)])((?: [^\\n]*)?(?:\\n|$))`);
 
           // Check if following lines should be included in List Item
+          let prevLine = line;
           while (src) {
             rawLine = src.split('\n', 1)[0];
+            prevLine = line;
             line = rawLine;
 
             // Re-align to follow commonmark nesting rules
             if (this.options.pedantic) {
               line = line.replace(/^ {1,4}(?=( {4})*[^ ])/g, '  ');
             }
 
+            if (this.rules.block.hr.test(line)) {
+              // End list if bullet was actually HR (possibly move into itemRegex?)
+              // make sure it is not a setext heading, which takes precedence
+              const twoLines = [prevLine, line].join('\n');
+              const matchLheadingPattern = this.rules.block.lheading.test(twoLines);
+              const lineIdentIsLargerThanPrev = line.search(/[^ ]/) >= indent;
+              const isNextLineSetextHeading = matchLheadingPattern && lineIdentIsLargerThanPrev;
+              if (!isNextLineSetextHeading) {
+                break;
+              }
+            }
+
             // End list item if found start of new bullet
             if (nextBulletRegex.test(line)) {
               break;