(#698): Put limit on feMorphology radii to prevent thread hang

Limits feMorphology radii to 10.0, a somewhat arbitrary number that I attempted to balance quickly (<1 second on a Ryzen system) opening eog and having a wide enough range for the effect. I tested various radius sizes by changing the svg in the linked issue before deciding on 10.

The examples for radius size I could find only had it go as high as 6, so I figured 10 would be safe. There is a bit of leeway for the size, as on my system it could go as high as 15 before eog tried to crash on moving or resizing the window (at 10 resizing is a bit slow, but usable). I tested it after compilation by overriding eog's library to use it and loading the 9999 radius file, which loaded as expected.

If there's something I've done wrong, or how I implemented it is odd for rust's, or this project's, conventions please let me know!

I'm an Outreachy applicant by the way, so I'm here to learn and will work on tackling more bugs or whatever is most needed for the next couple weeks! #698 (closed)