Problem:
If clipboard job exits by signal, the exit code is >=128:
939d9053bd
xclip 0.13 often exits with code 143, which spams unhelpful messages:
clipboard: error invoking xclip: Waiting for selection requests,
Control-C to quit Waiting for selection request number 1
Solution:
Don't show a warning if the clipboard tool exit code is >=128.
Fixes: #7054
c3de6524a5
