utils: add from_gchars

To copy into a std::string & free.

lib/utils/mu-utils.hh

@@ -130,6 +130,23 @@ std::string date_to_time_t_string(const std::string& date, bool first);
  */
 std::string date_to_time_t_string(int64_t t);
 
+/**
+ * Create a std::string by consuming a gchar* array; this takes ownership
+ * of str which should no longer be used.
+ *
+ * @param str a gchar* or NULL (latter taken as "")
+ *
+ * @return a std::string
+ */
+static inline std::string
+from_gchars(gchar*&& str)
+{
+	std::string s{str ? str : ""};
+	g_free(str);
+
+	return s;
+}
+
 using Clock    = std::chrono::steady_clock;
 using Duration = Clock::duration;