ringtones: customRingtone can be an absolute or relative path

Change-Id: I434255ea4caf66c630927bdfea572c49e7e1c658
GitLab: #748

src/account.cpp

@@ -289,9 +289,8 @@ Account::unserialize(const YAML::Node& node)
         // If the user defined a custom ringtone, the file may not exists
         // In this case, fallback on the default ringtone path (this will be set during the next
         // setAccountDetails)
-        auto pathRingtone = std::string(JAMI_DATADIR) + DIR_SEPARATOR_STR + RINGDIR
-                            + DIR_SEPARATOR_STR + ringtonePath_;
-        if (!fileutils::isFile(pathRingtone)) {
+        auto pathRingtone = fmt::format("{}/{}/{}", JAMI_DATADIR, RINGDIR, ringtonePath_);
+        if (!fileutils::isFile(ringtonePath_) && !fileutils::isFile(pathRingtone)) {
             JAMI_WARN("Ringtone %s is not a valid file", pathRingtone.c_str());
             ringtonePath_ = DEFAULT_RINGTONE_PATH;
         }