Common return value, when the time for a given frame is requested

[hinterwaeldler]

Hi,

while searching for something else i've found something strange in the return value of the getTime(int32_t frame) function implementation of the Asf, AvsProxy and the flv video demuxer. While the other demux return ADM_NO_PTS or ADM_COMPRESSED_NO_PTS (which is an alternative representation of the first) the three above return 0.
So changed them to ADM_NO_PTS and hope I got the meaning of the invalid time value correctly.

[mean]

indeed, legacy from older interface
Thanks & committed