content: Handle blank text nodes after code blocks

Fixes: #355

lib/model/content.dart

@@ -1124,14 +1124,18 @@ class _ZulipContentParser {
     return result;
   }
 
+  static final _redundantLineBreaksRegexp = RegExp(r'^\n+$');
+
   List<BlockContentNode> parseBlockContentList(dom.NodeList nodes) {
     assert(_debugParserContext == _ParserContext.block);
     final List<BlockContentNode> result = [];
     List<ImageNode> imageNodes = [];
     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 && _redundantLineBreaksRegexp.hasMatch(node.text)) {
+        continue;
+      }
 
       final block = parseBlockContent(node);
       if (block is ImageNode) {

test/model/content_test.dart

@@ -301,6 +301,17 @@ class ContentExample {
         '\n</code></pre></div>'),
     ]);
 
+  static const codeBlockFollowedByMultipleLineBreaks = ContentExample(
+    'blank text nodes after code blocks',
+    '    code block.\n\nsome content',
+    // https://chat.zulip.org/#narrow/stream/7-test-here/near/1774823
+    '<div class="codehilite">'
+      '<pre><span></span><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")]),
+    ]);
+
   static final mathInline = ContentExample.inline(
     'inline math',
     r"$$ \lambda $$",
@@ -865,6 +876,7 @@ void main() {
   testParseExample(ContentExample.codeBlockHighlightedMultiline);
   testParseExample(ContentExample.codeBlockWithHighlightedLines);
   testParseExample(ContentExample.codeBlockWithUnknownSpanType);
+  testParseExample(ContentExample.codeBlockFollowedByMultipleLineBreaks);
 
   testParseExample(ContentExample.mathBlock);
   testParseExample(ContentExample.mathBlockInQuote);