Show all targets for which corpora could not be generated

[smoelius]

Right now, cargo-test-fuzz stops immediately when it cannot generate a corpus for a fuzz target:

test-fuzz/cargo-test-fuzz/src/lib.rs

Lines 1325 to 1330 in 4e6e3ab

	ensure!(
	corpus_dir.exists(),
	"Could not find or auto-generate `{}`. Please ensure `{}` is tested.",
	corpus_dir.to_string_lossy(),
	target
	);

A better approach would be to try to generate a corpus for each fuzz target and, at the end, show the ones for which the operation failed.

I think this should be an easy change.

[HiteshMittal07]

@smoelius Just wanted to let you know that I’ll be working on this issue now.