stream_.lastTickTimestamp not initialized

[thestk]

stream_.lastTickTimestamp not initialized

[garyscavone]

I think I fixed this with commit #62f62cf90364040706863bd574d340e7c82216c3.

[sonoro1234]

If getStreamTime is called after startStream but when tickStreamTime is still not called by the callback ,lastTickTimestamp is too old.
I think that startStream should update lastTickTimestamp also.

[sonoro1234]

Just tried above idea with asio and works as expected.
To do a PR, the easiest way would be to modify RtAudio::startStream by adding

#if defined( HAVE_GETTIMEOFDAY )
  gettimeofday( &stream_.lastTickTimestamp, NULL );
#endif

but stream_ is not a member of RtAudio.

Instead of modifing each RtApi specialization of startStream perhaps all could be reworked: create RtApi:startStreamPre which would call gettimeofday and after RtApiSpecialization:startStream
and then call it from RtAudio:

RtApi::startStreamPre(void) {
    #if defined( HAVE_GETTIMEOFDAY )
      gettimeofday( &stream_.lastTickTimestamp, NULL );
    #endif
    rtapi_->startStream();
}
inline void RtAudio :: startStream( void ) { return rtapi_->startStreamPre(); }

@garyscavone what do you think about that?
@radarsat1