Don't crash when removing trailing whitespaces on pre-line blocks

Fix #610.

weasyprint/layout/preferred.py

@@ -703,11 +703,14 @@ def trailing_whitespace_size(context, box):
     if box.style['font_size'] == 0 or len(stripped_text) == len(box.text):
         return 0
     if stripped_text:
-        old_box, _, _ = split_text_box(context, box, None, 0)
+        resume = 0
+        while resume is not None:
+            old_resume = resume
+            old_box, resume, _ = split_text_box(context, box, None, resume)
         assert old_box
         stripped_box = box.copy_with_text(stripped_text)
         stripped_box, resume, _ = split_text_box(
-            context, stripped_box, None, 0)
+            context, stripped_box, None, old_resume)
         assert stripped_box is not None
         assert resume is None
         return old_box.width - stripped_box.width

weasyprint/tests/test_text.py

@@ -974,3 +974,12 @@ def test_text_transform():
     line5, = p5.children
     text5, = line5.children
     assert text5.text == 'hé lO1'
+
+
+@assert_no_logs
+def test_text_floating_pre_line():
+    # Test regression: https://github.com/Kozea/WeasyPrint/issues/610
+    page, = render_pages('''
+      <div style="float: left; white-space: pre-line">This is
+      oh this end </div>
+    ''')