Also short circuit prefix when there is an error already/so we get a single error

[ldemailly]

before:

$ grol -quiet -c '~~~1.1'
09:34:48.081 [ERR] Total 1 error:
<err: bitwise not of <err: bitwise not of <err: bitwise not of 1.1>>>

now

09:35:04.640 [ERR] Total 1 error:
<err: bitwise not of 1.1>