Mms: Process has stopped after dragging progress

testcase 1> create a slideshow mms and play it. Tap progress bar
                continuously until play finished.
         2> create a slideshow mms and play it. Tap progress bar
                continuously when rotate the screen

We have to set the seek bar change listener to null,otherwise if
the activity stop during tap progress bar continuously, window
will leak.

Change-Id: I206d35b91e04de06c2073c3fb0d9176da6adc81c
Author: Frederic Predon <frederic.predon@intel.com>
Signed-off-by: b533 <b533@borqs.com>
Signed-off-by: Frederic Predon <frederic.predon@intel.com>
Signed-off-by: Bin Yang <bin.y.yang@intel.com>
Signed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 28634