Fix loop condition in BidiRunList::replaceRunWithRuns

Source/platform/text/BidiRunList.h

Index: Source/platform/text/BidiRunList.h
diff --git a/Source/platform/text/BidiRunList.h b/Source/platform/text/BidiRunList.h
index bfaaab0de9cc576609802973d6cda072e7a29716..53df3d9314ebbd730ff6ae9b5ff1738e70fadfaa 100644
--- a/Source/platform/text/BidiRunList.h
+++ b/Source/platform/text/BidiRunList.h
@@ -153,7 +153,7 @@ void BidiRunList<Run>::replaceRunWithRuns(Run* toReplace, BidiRunList<Run>& newR
     } else {
         // Find the run just before "toReplace" in the list of runs.
         Run* previousRun = m_firstRun;
-        while (previousRun->next() != toReplace)
+        while (previousRun->next() && previousRun->next() != toReplace)
             previousRun = previousRun->next();
         ASSERT(previousRun);
         previousRun->setNext(newRuns.firstRun());