patch 8.2.0138: memory leak when starting a job fails

Problem:    Memory leak when starting a job fails.
Solution:   Free the list of arguments. (Ozaki Kiichi, closes #5510)
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index 4dac7aa..dace45b 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -1977,3 +1977,8 @@
   call assert_match("%s%s", text[2])
   call delete('Xlog')
 endfunc
+
+func Test_job_start_fails()
+  " this was leaking memory
+  call assert_fails("call job_start([''])", "E474:")
+endfunc