Bugfix ofxAssimpAdvancedExample HDR

[NickHardeman]

Fix for loading an HDR image instead of EXR and added toggles for controlling the cube map.
#8346

[dimitre]

I've just listed all exr present in examples

find . -name '*.exr'

./3d/ofxAssimpAdvancedExample/bin/data/kloppenheim_06_puresky_1k.exr
./3d/ofxAssimpExample/bin/data/securityCamera.fbm/security_camera_02_metal_1k.exr
./3d/ofxAssimpExample/bin/data/securityCamera.fbm/security_camera_02_rough_1k.exr
./3d/ofxAssimpExample/bin/data/securityCamera.fbm/security_camera_02_nor_gl_1k.exr
./graphics/floatingPointImageExample/bin/data/nyc-small.exr

[NickHardeman]

@dimitre Thank you. Submitted a PR (#8350) for the ofxAssimpExample.