Add null position check in SpellChecker::findFirstMisspelling

third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.cpp

Index: third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.cpp
diff --git a/third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.cpp b/third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.cpp
index 4371ed59c482a569009a567a77cff31b4a478775..27ae01b469ee1bcd7552b7758d107ab3ae2a253d 100644
--- a/third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.cpp
+++ b/third_party/WebKit/Source/core/editing/spellcheck/SpellChecker.cpp
@@ -1158,6 +1158,9 @@ std::pair<String, int> SpellChecker::findFirstMisspelling(const Position& start,
       break;
     VisiblePosition newParagraphStart =
         startOfNextParagraph(createVisiblePosition(paragraphEnd));
+    if (newParagraphStart.isNull())
+      break;
+
     paragraphStart = newParagraphStart.toParentAnchoredPosition();
     paragraphEnd = endOfParagraph(newParagraphStart).toParentAnchoredPosition();
     firstIteration = false;