get_exif_date_time_offset: Prioritize QuickTime:ContentCreateDate over EXIF:DateTimeOriginal for videos.

[oPromessa]

I found some videos (from Canon Cameras) which:

• have EXIF:DateTimeOriginal without offset fields
• and QuickTime:ContentCreateDate with offset.

With this code change we give priority to QuickTime:ContentCreateDate for videos.

PS: maybe not the most elegant code!

[RhetTbull]

@oPromessa Thanks for this. Is there any reason not to just list the QuickTime fields first rather than test for photo/video and construct a list in a different order? Photos won't have the QuickTime:ContentCreateDate so it will be ignored?

Also, in the future, please run black on the code before submitting the PR. This will fix formatting such as mixed use of single and double quotes. I'll add a note to the README_DEV.md about this.

[oPromessa]

Let me review.

Will start using black. Thanks for there heads up.