Movie play following Open Source crash editor when changing viewport size.

When playing movie in PIE, changing viewport size leads to Engine crash.
This is not reproduced in 4.14.3

1) Import large size movie(FHD)
2) Create a Movie player, media texture, material, cube
3) Apply the material over cube, place it on level.
4) Call Blueprint function 'Open Source' to play movie in level blueprint
5) Play game in Editor. Notice movie is played on the cube.
6) Press F11 key several times, notice the Engine crash. (If not, try other movie)

Reproduced with following movie spec: recorded with Galaxy S7
Full HD(1920x1280)
AVC1, 24bit - FFmpeg(h264)