libsaria: Get the path to the pipe file

This will either return the full path to the file or an empty string if
no pipe has been created.

include/libsaria/path.h

@@ -19,5 +19,6 @@ string get_saria_dir();
 void make_saria_dir();
 bool exists(string);
 sid_t lookup_songid(string &);
+string get_pipe_file();
 
 #endif /* LIBSARIA_PATH_H */

libsaria/path/dir.cpp

@@ -62,3 +62,13 @@ sid_t lookup_songid(string &filepath)
 		return err;
 	return stat.st_ino;
 }
+
+string get_pipe_file()
+{
+	struct stat stat;
+	string file = get_saria_dir() + "/saria.pipe";
+
+	if (lstat(file.c_str(), &stat) != 0)
+		return "";
+	return file;
+}