Iterate from array copy in latestExperimentStartTimestampBetweenTimestamp: (#3764)

Author: christibbs

FirebaseABTesting/Sources/FIRExperimentController.m

@@ -246,7 +246,7 @@ - (void)updateExperimentsWithServiceOrigin:(NSString *)origin
 
 - (NSTimeInterval)latestExperimentStartTimestampBetweenTimestamp:(NSTimeInterval)timestamp
                                                      andPayloads:(NSArray<NSData *> *)payloads {
-  for (NSData *payload in payloads) {
+  for (NSData *payload in [payloads copy]) {
     ABTExperimentPayload *experimentPayload = ABTDeserializeExperimentPayload(payload);
     if (!experimentPayload) {
       FIRLogInfo(kFIRLoggerABTesting, @"I-ABT000002",