logger: fix file open issue if crypto algorithm is disabled

Create empty file even if crypto key is not stored into the beginning
of the log file to allow file logger to always append log data into
existing file.

src/modules/logger/log_writer_file.cpp

@@ -92,6 +92,16 @@ bool LogWriterFile::init_logfile_encryption(const char *filename)
 {
 	if (_algorithm == CRYPTO_NONE) {
 		_min_blocksize = 1;
+
+		// No encryption, just create empty log file
+		int fd = ::open((const char *)filename, O_CREAT | O_WRONLY | O_DIRECT | O_SYNC, PX4_O_MODE_666);
+
+		if (fd < 0) {
+			PX4_ERR("Can't open log file, errno: %d", errno);
+			return false;
+		}
+
+		::close(fd);
 		return true;
 	}