fix(markdown): fix empty block handling (#843)

Signed-off-by: Panos Vagenas <35837085+vagenas@users.noreply.github.com>

tests/data/groundtruth/docling_v2/blocks.md.md

@@ -0,0 +1,33 @@
+Unordered list:
+
+- foo
+
+Empty unordered list:
+
+Ordered list:
+
+- bar
+
+Empty ordered list:
+
+Heading:
+
+# my heading
+
+Empty heading:
+
+Indented code block:
+
+```
+print("Hi!")
+```
+
+Empty indented code block:
+
+Fenced code block:
+
+```
+print("Hello world!")
+```
+
+Empty fenced code block:

tests/data/md/blocks.md

@@ -0,0 +1,43 @@
+Unordered list:
+
+- foo
+
+Empty unordered list:
+
+-
+
+Ordered list:
+
+1. bar
+
+Empty ordered list:
+
+1.
+
+Heading:
+
+# my heading
+
+Empty heading:
+
+#
+
+Indented code block:
+
+    print("Hi!")
+
+Empty indented code block:
+
+    
+
+Fenced code block:
+
+```python
+print("Hello world!")
+```
+
+Empty fenced code block:
+
+```
+
+```