Addition to proxydeps in Mk/Scripts/qa.sh: print an error on non-existent dependency

[yuri_rawbw.com]

Summary

Flawed ports's build process created the library that is linked to non-existent dynamic library:

ldd -a work/stage//usr/local/lib/lv2/convo.lv2/convoLV2.so

work/stage//usr/local/lib/lv2/convo.lv2/convoLV2.so:
libzita-convolver.so.3 => not found (0)

Currently, proxydeps misses such situation. I made it to print an error message in such case.

[yuri_rawbw.com]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=221197

[yuri_rawbw.com]

Added comment.