Don't try to move non visible contents in "Indent" command

Source/core/editing/IndentOutdentCommand.cpp

Index: Source/core/editing/IndentOutdentCommand.cpp
diff --git a/Source/core/editing/IndentOutdentCommand.cpp b/Source/core/editing/IndentOutdentCommand.cpp
index d1a4480a91172acb064a3d55e1bbb72fed91d64e..4caef802ed471640118f5a779199879c7b34bc70 100644
--- a/Source/core/editing/IndentOutdentCommand.cpp
+++ b/Source/core/editing/IndentOutdentCommand.cpp
@@ -121,7 +121,10 @@ void IndentOutdentCommand::indentIntoBlockquote(const Position& start, const Pos
         startOfContents = VisiblePosition(positionInParentAfterNode(*targetBlockquote));
     }
 
-    moveParagraphWithClones(startOfContents, VisiblePosition(end), targetBlockquote.get(), outerBlock.get());
+    VisiblePosition endOfContents(end);
+    if (startOfContents.isNull() || endOfContents.isNull())
+        return;
+    moveParagraphWithClones(startOfContents, endOfContents, targetBlockquote.get(), outerBlock.get());
 }
 
 void IndentOutdentCommand::outdentParagraph()