Merge pull request #1507 in FS/freeswitch from ~DRAGOS_OANCEA_NX/freeswitch-dragos-nx:bugfix/FS-11105/multichannel_prebuf_datalen to master

* commit '6bc59b3b':
  FS-11105: core: fix in switch_core_file_write() for audio channels > 2 ( eg: for when the prebuffer size does not divide by the number of wanted channels)