output/analog: track and free memory for float conversion buffer

output/analog: track and free memory for float conversion buffer

==18779== 800,000 bytes in 196 blocks are definitely lost in loss record 29 of 29
==18779==    at 0x4C29110: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==18779==    by 0x4E635C3: receive (analog.c:319)
==18779==    by 0x40870B: datafeed_in (session.c:316)
==18779==    by 0x4E59D4E: sr_session_send (session.c:1201)
==18779==    by 0x4E59F8B: sr_session_send (session.c:1159)
==18779==    by 0x4E62595: send_chunk (wav.c:234)
==18779==    by 0x4E62A06: process_buffer (wav.c:290)
==18779==    by 0x40954A: load_input_file_module (input.c:123)
==18779==    by 0x4097AB: load_input_file (input.c:157)
==18779==    by 0x40531E: main (main.c:288)