fix several errors/warnings which only appear with -O3

src/decode.c

@@ -342,6 +342,8 @@ static void * decoder_task(void *arg)
 			decoder_sleep(dc);
 		}
 	}
+
+	return NULL;
 }
 
 void decoderInit(DecoderControl * dc)

src/inputStream_http.c

@@ -721,7 +721,7 @@ int inputStream_httpSeek(InputStream * inStream, long offset, int whence)
 
 static void parseIcyMetadata(InputStream * inStream, char *metadata, int size)
 {
-	char *r;
+	char *r = NULL;
 	char *s;
 	char *temp = xmalloc(size + 1);
 	memcpy(temp, metadata, size);