fix format parameter bug discovered by Go 1.11

This must have been a really old one, but apparently hasn't really
been triggered all the time. Edge case anyway.

olu/object-less-utils.go

@@ -155,7 +155,7 @@ func RuneSubstr(s string, start, end int) string {
 					" for string of length %d (\"%s\")",
 					start, len(s), s)
 			}
-			msg.Bailf("reading from string \"%s\": %v", err)
+			msg.Bailf("reading from string \"%s\": %v", s, err)
 		}
 	}
 	for ; si < end || end < 0; si++ {
@@ -171,7 +171,7 @@ func RuneSubstr(s string, start, end int) string {
 						end, len(s), s)
 				}
 			}
-			msg.Bailf("reading from string \"%s\": %v", err)
+			msg.Bailf("reading from string \"%s\": %v", s, err)
 		}
 		nbuf.WriteRune(r)
 	}