[gnumeric] don't crash if ssconvert_set_cells is NULL

[Jean Bréfort <jbrefort src gnome org>]

commit a33bd44b14e42036ed01a24f1539c663f22eb5c7
Author: Jean Brefort <jean brefort normalesup org>
Date:   Mon Feb 24 18:20:19 2020 +0100

    don't crash if ssconvert_set_cells is NULL

 ChangeLog       | 4 ++++
 src/ssconvert.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/ChangeLog b/ChangeLog
index fb6276d49..98068aa85 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2020-02-24  Jean Brefort  <jean brefort normalesup org>
+
+       * src/ssconvert.c (convert):  don't crash if ssconvert_set_cells is NULL.
+
 2019-11-12  Morten Welinder  <terra gnome org>
 
        * src/gui-util.c (gnm_restore_window_geometry): Something changed
diff --git a/src/ssconvert.c b/src/ssconvert.c
index 056ba33e3..96302d109 100644
--- a/src/ssconvert.c
+++ b/src/ssconvert.c
@@ -1021,7 +1021,7 @@ convert (char const *inarg, char const *outarg, char const *mergeargs[],
                wbv = workbook_view_new_from_uri (infile, fo,
                                                  io_context,
                                                  ssconvert_import_encoding);
-               if (apply_updates (wbv)) {
+               if ((ssconvert_set_cells != NULL) && apply_updates (wbv)) {
                        res = 1;
                        goto out;
                }