Update GTLRService.m (#191)

Fix static analysis warning
`GTLRService.m:2477:26: Converting a pointer value of type 'NSNumber * _Nullable' to a primitive boolean value; instead, either compare the pointer to nil or call -boolValue`

Source/Objects/GTLRService.m

@@ -2474,7 +2474,7 @@ - (instancetype)initWithService:(GTLRService *)service
     _objectClassResolver = params.objectClassResolver ?: service.objectClassResolver;
 
     _retryEnabled = ((params.retryEnabled != nil) ? params.retryEnabled.boolValue : service.retryEnabled);
-    _maxRetryInterval = (params.maxRetryInterval ?
+    _maxRetryInterval = ((params.maxRetryInterval != nil) ?
                          params.maxRetryInterval.doubleValue : service.maxRetryInterval);
     _shouldFetchNextPages = ((params.shouldFetchNextPages != nil)?
                              params.shouldFetchNextPages.boolValue : service.shouldFetchNextPages);