When opening a PCM wave file for reading, we aren't tracking the
frequency of the opened file, so we treat 16khz files as 8khz and do
half reads.
This patch also cleans up some of the data types and an unnecessarily
complex `if` expression.
ASTERISK-26613 #close
Reported by: Vitaly K
Change-Id: I05f8b263058dc573ea8ffe0c62e7964506e11815