Add routine for checking startTime when start the next utterance in handleSpeakingCompleted()

Source/modules/speech/SpeechSynthesis.cpp

Index: Source/modules/speech/SpeechSynthesis.cpp
diff --git a/Source/modules/speech/SpeechSynthesis.cpp b/Source/modules/speech/SpeechSynthesis.cpp
index 2c91a7aab62d4126d2c7e688190571581f6c8f9f..82949cea75c27c921ded5c8c0c9c53e80955ada0 100644
--- a/Source/modules/speech/SpeechSynthesis.cpp
+++ b/Source/modules/speech/SpeechSynthesis.cpp
@@ -168,7 +168,7 @@ void SpeechSynthesis::handleSpeakingCompleted(SpeechSynthesisUtterance* utteranc
     fireEvent(errorOccurred ? EventTypeNames::error : EventTypeNames::end, utterance, 0, String());
 
     // Start the next utterance if we just finished one and one was pending.
-    if (didJustFinishCurrentUtterance && !m_utteranceQueue.isEmpty())
+    if (didJustFinishCurrentUtterance && !m_utteranceQueue.isEmpty() && !utterance->startTime())
         startSpeakingImmediately();
 }