Don't fail if missing dependency is in excludeLibraryPatterns

[remleduff]

We're trying to build an AppImage with one specific library that is excluded so that it comes from the host rather than the AppImage, using the --exclude command line option.

However, our CI build systems don't include that library at all, and this fails with:

ERROR: Could not find dependency: libcuda.so.1 
ERROR: Failed to deploy dependencies for existing files 

This is unfortunate, because libcuda.so.1 was excluded, and not expected to be part of the appimage in the first place.

Making this a warning allows our build to succeed, and the resulting AppImage uses libcuda from the host as expected.

(This addresses the issue from #225)

[TheAssassin]

Thanks!