grep: Fix two memory leaks

We duplicate the grep_opt structure when using grep threads, but didn't
later free either the patterns attached to this new structure or the
structure itself.

Signed-off-by: Dan McGee <dpmcgee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-grep.c

@@ -205,6 +205,8 @@ static void *run(void *arg)
 
 		work_done(w);
 	}
+	free_grep_patterns(arg);
+	free(arg);
 
 	return (void*) (intptr_t) hit;
 }