Fix Division By Zero Warning for Focal Length

[jaywilliams]

If a file has invalid EXIF data, it can cause an division by zero warning to occur.

[Miljar]

Hi Jay,

Thanks for your PR. Can you please provide a unit test for this?

[jaywilliams]

I've added a unit test, but whenever I try to run any tests, I get a notice No tests executed!, so I'm unsure how to fully test my test.

[Miljar]

You should specify the configuration file to be used. In travis, it works like this:

php vendor/bin/phpunit -c phpunit.xml.dist

[jaywilliams]

Thanks, Tom. I was able to run the unit tests, and can confirm that it works properly.

[Miljar]

Thanks Jay, will merge & release!