fix(asciidoc): set default size when missing in image directive (#1769)

The AsciiDoc backend should not create an ImageRef with Size equal to None, instead use default size values.
Refactor static methods as such and add the staticmethod decorator.
Extend the regression test for this fix.

Signed-off-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>

tests/test_backend_asciidoc.py

@@ -2,7 +2,11 @@ import glob
 import os
 from pathlib import Path
 
-from docling.backend.asciidoc_backend import AsciiDocBackend
+from docling.backend.asciidoc_backend import (
+    DEFAULT_IMAGE_HEIGHT,
+    DEFAULT_IMAGE_WIDTH,
+    AsciiDocBackend,
+)
 from docling.datamodel.base_models import InputFormat
 from docling.datamodel.document import InputDocument
 
@@ -18,6 +22,24 @@ def _get_backend(fname):
     return doc_backend
 
 
+def test_parse_picture():
+    line = (
+        "image::images/example1.png[Example Image, width=200, height=150, align=center]"
+    )
+    res = AsciiDocBackend._parse_picture(line)
+    assert res
+    assert res.get("width", 0) == "200"
+    assert res.get("height", 0) == "150"
+    assert res.get("uri", "") == "images/example1.png"
+
+    line = "image::renamed-bookmark.png[Renamed bookmark]"
+    res = AsciiDocBackend._parse_picture(line)
+    assert res
+    assert "width" not in res
+    assert "height" not in res
+    assert res.get("uri", "") == "renamed-bookmark.png"
+
+
 def test_asciidocs_examples():
     fnames = sorted(glob.glob("./tests/data/asciidoc/*.asciidoc"))