markdown: Fix bullet list indentation bug.

Previously, the frontend-only javascript processor didn't show the
same output as the backend for unordered lists in case of odd
indentation before the bullet indicator, resulting in wrong output
shown in drafts. This is because their was no specific way to handle
odd indentation.

Fix for it was to check for odd indentation whenever bullet list is
encountered and trim a space to make it even and ideal for zulip's
markdown.

Fixes zulip#10966

static/third/marked/lib/marked.js

@@ -272,6 +272,10 @@ Lexer.prototype.token = function(src, top, bq) {
       src = src.substring(cap[0].length);
       bull = cap[2];
 
+      // Reduces the odd number of spaces
+      // to even.
+      cap[0] = cap[0].replace(/^((  )*) ?/gm, "$1");
+
       this.tokens.push({
         type: 'list_start',
         ordered: bull.length > 1

zerver/tests/fixtures/markdown_test_cases.json

@@ -168,6 +168,12 @@
       "marked_expected_output": "<ul>\n<li>I am outer list<br>\nI am something inside</li>\n</ul>",
       "text_content": "\nI am outer list\n  I am something inside\n"
     },
+    {
+      "name": "ulist_nested_ulist_with_odd_even_space_indent",
+      "input": "Nested list\n* I am outer list first item\n * I am outer list second item\n   * I am inner nested list first item",
+      "expected_output": "<p>Nested list</p>\n<ul>\n<li>I am outer list first item</li>\n<li>I am outer list second item<ul>\n<li>I am inner nested list first item</li>\n</ul>\n</li>\n</ul>",
+      "text_content": "Nested list\n\nI am outer list\nI am inner nested list first item\nI am inner nested list second item\n\n\n"
+    },
     {
       "name": "ulist_codeblock",
       "input": "~~~\nint x = 3\n* 4;\n~~~",