pulsesink: fix buffer overflow if the writing position exceeds the maximum length of pulse audio buffer.
requested to merge elliot_chen/gstreamer:pulsesink-avoid-writing-data-that-exceeds-the-buffer-size into main
- For some streams such as WMV, the AV interleave is large. The timestamp of first audio buffer may far behand the seek position if do seek operation. It will cause pulse audio buffer overflow and lost the audio buffer.
- Need check the position of the data to be written. If it's greater than the maximum buffer length, need write silent data firstly in the current write index to avoid overflow.