patch 8.0.1569: warning for uninitialized variable from gcc

Problem:    Warning for uninitialized variable from gcc.
Solution:   Initialize the variable.
diff --git a/src/quickfix.c b/src/quickfix.c
index 23cb926..7ee386d 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -4099,7 +4099,7 @@
     win_T	*wp = NULL;
     qf_info_T	*qi = &ql_info;
     char_u	*au_name = NULL;
-    int		save_qfid;
+    int		save_qfid = 0;  // init for gcc
     int		res;
 
     switch (eap->cmdidx)