`git grep` error `signal: killed`

[KN4CK3R]

If a search query produces more then 50 results the grep call is canceled which results in a signal: killed error from scanner.Err().

@wxiaoguang

[wxiaoguang]

Oh yes, you are right, I'm on it now

[wxiaoguang]

Fix git grep search limit, add test #30071

Added a test, without the fix, the test fails with "signal: killed"