Clicking 'Seek Backward' increases the (negative) speed shown on the preview tab label indefinetely

[Rodrigo Castelan Carlson]

OpenShot 1.3.1~alpha1

Seek Backward (tlbSeekBackward) clicked

- Observed:
The (negative) speed increases at each click. The preview tab label is updated accordingly to show the present speed: "Video Preview (-1X)", -2X, ... Even if the video is at the beggining of the track, it keeps increasing the (negative) speed on the preview tab label.

- Expected:
The (negative) speed increases at each click as long as the preview is playing (backward). The preview tab label is updated accordingly to show the present speed "Video Preview (-1X)", -2X, ... If the cursor is at (or reaches) the beginning of the (timeline) the preview tab label should be "Video Preview". The button should be disabled at this position, as keeping the button enabled does not serve any purpose.

[Olivier Girard (eolinwen)]

Hi,
I linked this thread on the thread open for the tests done for this version : https://bugs.launchpad.net/openshot/+bug/730268
Thanks.