Rearrange player cleanup code

Since apparently closing stdin and later calling communicate() is no bueno, 
we're just going to rearrange the process finalization code so both cleanup()
and the pipe loop exit conditions point to it.

discord/player.py

@@ -155,7 +155,7 @@ def __init__(self, source: Union[str, io.BufferedIOBase], *, executable: str = '
         self._pipe_thread: Optional[threading.Thread] = None
 
         if piping:
-            n = f'PopenStdinWriter:{id(self):#x}'
+            n = f'popen-stdin-writer:{id(self):#x}'
             self._stdin = self._process.stdin
             self._pipe_thread = threading.Thread(target=self._pipe_writer, args=(source,), daemon=True, name=n)
             self._pipe_thread.start()
@@ -172,22 +172,7 @@ def _spawn_process(self, args: Any, **subprocess_kwargs: Any) -> subprocess.Pope
         else:
             return process
 
-    def _pipe_writer(self, source: io.BufferedIOBase) -> None:
-        while self._process:
-            # arbitrarily large read size 
-            data = source.read(8192)
-            if not data:
-                self._stdin.close() # EOF
-                break
-            try:
-                self._stdin.write(data)
-            except Exception:
-                _log.debug('Write error for %s, this is probably not a problem', self, exc_info=True)
-                # at this point the source data is either exhausted or the process is fubar
-                self._stdin.close()
-                break
-
-    def cleanup(self) -> None:
+    def _kill_process(self) -> None:
         proc = self._process
         if proc is MISSING:
             return
@@ -206,7 +191,25 @@ def cleanup(self) -> None:
         else:
             _log.info('ffmpeg process %s successfully terminated with return code of %s.', proc.pid, proc.returncode)
 
-        self._process = self._stdout = MISSING
+
+    def _pipe_writer(self, source: io.BufferedIOBase) -> None:
+        while self._process:
+            # arbitrarily large read size
+            data = source.read(8192)
+            if not data:
+                self._process.terminate()
+                return
+            try:
+                self._stdin.write(data)
+            except Exception:
+                _log.debug('Write error for %s, this is probably not a problem', self, exc_info=True)
+                # at this point the source data is either exhausted or the process is fubar
+                self._process.terminate()
+                return
+
+    def cleanup(self) -> None:
+        self._kill_process()
+        self._process = self._stdout = self._stdin = MISSING
 
 class FFmpegPCMAudio(FFmpegAudio):
     """An audio source from FFmpeg (or AVConv).