Better timeseek on resume files

Timeseek was broken with resume files:
-When a resume file was started, it returned 00:00:00 position to
renderer, making very difficult to someone to know what position the
resume seeks to, because renderer thinks it's playing from the beginning
-If someone wants to seek the file, it's necessary to use relative
position, because 00:00:00 in player was the resume position, which is
very annoying
-If someone stops playing the resume file before it ends, UMS will
record the relative position, not the real position in file