Don’t crash when out-of-flow box is split in out-of-flow parent

This code is not handled correctly. This commit avoids the crash, but it
doesn’t give a correct result. We have two different problems to solve:

- floats in floats are broken;
- split out-of-flow elements in split out-of-flow elements are broken.

Fix #1807 (but doesn’t give the right result).

Author: liZe

tests/draw/test_float.py

@@ -821,3 +821,40 @@ def test_float_split_14(assert_pixels):
         a
         <div style="float: left"><p>aa<p>aa</div>
         <div style="float: right"><p>bb<p>bb</div>''')
+
+
+@pytest.mark.xfail
+@assert_no_logs
+def test_float_split_15(assert_pixels):
+    assert_pixels('''
+        BB__RRRRRRRRRR__
+        BB__RRRRRRRRRR__
+        BB__RRRRRRRRRR__
+        BB__RRRRRRRRRR__
+        GGBBRRRRRRRRRR__
+        GGBBRRRRRRRRRR__
+        GGBBRRRRRRRRRR__
+        GGBBRRRRRRRRRR__
+        RRRRRRRRRR______
+        RRRRRRRRRR______
+    ''', '''
+        <style>
+            @font-face {src: url(weasyprint.otf); font-family: weasyprint}
+            @page {
+                size: 16px 2px;
+            }
+            body {
+                color: red;
+                font-family: weasyprint;
+                font-size: 2px;
+                line-height: 1;
+            }
+        </style>
+        <div style="float: left; position: relative; color: blue; width: 4px">
+          a a a
+          <div style="float: left; color: lime; width: 2px">
+            a a
+          </div>
+          a a
+        </div>
+        <div>bbbbb bbbbb bbbbb bbbbb bbbbb</div>''')

weasyprint/layout/page.py

@@ -567,6 +567,7 @@ def make_page(context, root_box, page_type, resume_at, page_number,
     out_of_flow_boxes = []
     broken_out_of_flow = {}
     context_out_of_flow = context.broken_out_of_flow.values()
+    context.broken_out_of_flow = broken_out_of_flow
     for box, containing_block, skip_stack in context_out_of_flow:
         box.position_y = root_box.content_box_y()
         if box.is_floated():
@@ -582,7 +583,6 @@ def make_page(context, root_box, page_type, resume_at, page_number,
         if out_of_flow_resume_at:
             broken_out_of_flow[out_of_flow_box] = (
                 box, containing_block, out_of_flow_resume_at)
-    context.broken_out_of_flow = broken_out_of_flow
     root_box, resume_at, next_page, _, _, _ = block_level_layout(
         context, root_box, 0, resume_at, initial_containing_block,
         page_is_empty, positioned_boxes, positioned_boxes, adjoining_margins)