All black image produces OpenCV error

[gfiumara]

Providing an all black image results in:

Error: NFIQ2 computeQualityScore returned an error code: Cannot compute Frequency Domain Analysis (FDA): OpenCV(4.5.3) /Users/gfiumara/git/NFIQ2/opencv/modules/core/src/mean.dispatch.cpp:516: error: (-215:Assertion failed) !_src.empty() in function 'meanStdDev'

We can likely catch this error before calling meanStdDev and provide a better error message.

Not necessarily a bug since there's no friction ridge data.