patch 8.2.4958: a couple conditions are always true

Problem:    A couple conditions are always true.
Solution:   Remove the conditions. (Goc Dundar, closes #10428)
diff --git a/src/quickfix.c b/src/quickfix.c
index aab1683..dde3f9d 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -2494,7 +2494,7 @@
     // store directory on the stack
     if (vim_isAbsName(dirbuf)
 	    || (*stackptr)->next == NULL
-	    || (*stackptr && is_file_stack))
+	    || is_file_stack)
 	(*stackptr)->dirname = vim_strsave(dirbuf);
     else
     {