lib/suitar: make some Reader.Next errors sticky

Updates PR #179

lib/suitar/suitar.go

diff --git a/lib/suitar/suitar.go b/lib/suitar/suitar.go
index 27ec692..6bb103d 100644
--- a/lib/suitar/suitar.go
+++ b/lib/suitar/suitar.go
@@ -552,10 +552,12 @@
 	}
 
 	if _, err := readFullNoEOF(r.r, r.block[:0x200]); err != nil {
+		r.err = err
 		return Header{}, err
 	}
 	typeflag, size, mode, modTime, err := parseBlock1(&r.block)
 	if err != nil {
+		r.err = err
 		return Header{}, err
 	}