FIX: checklist weren't working if there was an image URL

When clicking a "checklist", we're parsing the raw to change the state of the checklist that was clicked. If there was an image URL with an empty alternative text in the raw "![](https://example.com/image.jpg)" it would consider the "[]" as an empty checklist item.

Internal - t/124499

plugins/checklist/assets/javascripts/discourse/initializers/checklist.js

@@ -124,13 +124,19 @@ export function checklistSyntax(elem, postDecorator) {
         // make the first run go to index = 0
         let nth = -1;
         let found = false;
+
         const newRaw = post.raw.replace(
-          /\[(\s|\_|\-|\x|\\?\*)?\]/gi,
+          /\[( |x)?\]/gi,
           (match, ignored, off) => {
             if (found) {
               return match;
             }
 
+            // skip empty image URLs - "![](https://example.com/image.jpg)"
+            if (off > 0 && post.raw[off - 1] === "!") {
+              return match;
+            }
+
             nth += blocks.every(
               (b) => b[0] >= off + match.length || off > b[1]
             );

plugins/checklist/assets/javascripts/lib/discourse-markdown/checklist.js

@@ -1,4 +1,4 @@
-const REGEX = /\[(\s?|x|X)\]/g;
+const REGEX = /\[( |x)?\]/gi;
 
 function getClasses(str) {
   switch (str) {

plugins/checklist/test/javascripts/lib/checklist-test.js

@@ -38,6 +38,19 @@ acceptance("discourse-checklist | checklist", function (needs) {
     ]);
   });
 
+  test("does not check an image URL", async function (assert) {
+    const [$elem, updated] = await prepare(`
+![](upload://zLd8FtsWc2ZSg3cZKIhwvhYxTcn.jpg)
+[] first
+[] second
+    `);
+
+    $elem.find(".chcklst-box")[0].click();
+
+    const output = await updated;
+    assert.ok(output.includes("[x] first"));
+  });
+
   test("make checkboxes readonly while updating", async function (assert) {
     const [$elem, updated] = await prepare(`
 [ ] first