Never move unbreakable blocks that are at the top of a column / page.

Source/core/layout/LayoutBlockFlow.cpp

Index: Source/core/layout/LayoutBlockFlow.cpp
diff --git a/Source/core/layout/LayoutBlockFlow.cpp b/Source/core/layout/LayoutBlockFlow.cpp
index aadf77050085befb9e4b45132a7b5d0a17cb1119..c9aaf9d18baabbfc115ff8696bef66f54b525fc8 100644
--- a/Source/core/layout/LayoutBlockFlow.cpp
+++ b/Source/core/layout/LayoutBlockFlow.cpp
@@ -854,7 +854,9 @@ LayoutUnit LayoutBlockFlow::adjustForUnsplittableChild(LayoutBox& child, LayoutU
     if (!pageLogicalHeight)
         return logicalOffset;
     LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, AssociateWithLatterPage);
-    if (remainingLogicalHeight < childLogicalHeight)
+    // Break if there's not enough space left for us, but only as long as we're not already at the
+    // top of a page. No point in leaving a page completely blank.
+    if (remainingLogicalHeight < childLogicalHeight && remainingLogicalHeight < pageLogicalHeight)
         return logicalOffset + remainingLogicalHeight;
     return logicalOffset;
 }