content: Handle blank text nodes after code blocks

Fixes: zulip#355

Author: Khader-1

lib/model/content.dart

@@ -1107,7 +1107,7 @@ class _ZulipContentParser {
     for (final node in nodes) {
       // We get a bunch of newline Text nodes between paragraphs.
       // A browser seems to ignore these; let's do the same.
-      if (node is dom.Text && (node.text == '\n')) continue;
+      if (node is dom.Text && RegExp(r'^(\n+)$').hasMatch(node.text)) continue;
 
       final block = parseBlockContent(node);
       if (block is ImageNode) {

test/model/content_test.dart

@@ -521,6 +521,21 @@ class ContentExample {
       blockUnimplemented('more text'),
     ]]),
   ]);
+
+  static const lineBreaksAfterCodeBlocks = ContentExample(
+    'blank text nodes after code blocks',
+    '    code block''\n\n''some content',
+    '<div class="codehilite">'
+      '<pre><code>'
+        'code block.\n'
+      '</code></pre>'
+    '</div>\n\n'
+    '<p>'
+      'some content'
+    '</p>', [
+      CodeBlockNode([CodeBlockSpanNode(text: "code block.", type: CodeBlockSpanType.text)]),
+      ParagraphNode(links: null, nodes: [TextNode("some content")]),
+  ]);
 }
 
 UnimplementedBlockContentNode blockUnimplemented(String html) {
@@ -875,6 +890,8 @@ void main() {
       ]]),
     ]);
 
+    testParseExample(ContentExample.lineBreaksAfterCodeBlocks);
+
   test('all content examples are tested', () {
     // Check that every ContentExample defined above has a corresponding
     // actual test case that runs on it.  If you've added a new example