baseparse: provides pts/dts if valid
In the case of subframe decoding, the buffer pts/dts can have the same value as the previous buffer. We should keep at least the value instead of having GST_CLOCK_TIME_NONE for the output buffer.
This case happened with jpeg2000parse and stripes support such as
videotestsrc num-buffers=4 ! openjpegenc num-stripes=2 ! jpeg2000parse ! openjpegdec ! videoconvert ! autovideosink