Fix for em-size detection when loading font from .cff file.

For some type 1 font who had an original em-size of 2048, "forcing" the
em-size to 1000 can cause issues (e.g stretching of the font...)
The only way I found to detect that the original em-size was higher than
1000, is by using an estimation deduced from the Bounding Box.
This is a dirty hack, but it solved the problem for my case, and it did
not seem to trigger any problem with other fonts for now.
Test files for mis-detected em-size.

running the python test will generate a ttf font in tests/reslults.
Without the fix, this font will have an em-size smaller than it's glyph
size.