producer_sdl_image.c: Fix crash when attempting to play a folder without images

[melted] / profiles / square_ntsc_wide

description=Square NTSC Widescreen
frame_rate_num=30000
frame_rate_den=1001
width=854
height=480
progressive=1
sample_aspect_num=1
sample_aspect_den=1
display_aspect_num=16
display_aspect_den=9