[gnome-software] trivial: update dialog: Don't warn when update version isn't set

[Kalev Lember <klember src gnome org>]

commit abc724f3127c1e3797bf0f4193c0a1a7c0de3c16
Author: Kalev Lember <klember redhat com>
Date:   Tue Apr 10 15:39:03 2018 +0200

    trivial: update dialog: Don't warn when update version isn't set

 src/gs-update-dialog.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/gs-update-dialog.c b/src/gs-update-dialog.c
index 2509831f..7f7f80ea 100644
--- a/src/gs-update-dialog.c
+++ b/src/gs-update-dialog.c
@@ -362,6 +362,9 @@ is_downgrade (const gchar *evr1,
        g_autofree gchar *release1 = NULL;
        g_autofree gchar *release2 = NULL;
 
+       if (evr1 == NULL || evr2 == NULL)
+               return FALSE;
+
        /* split into epoch-version-release */
        if (!gs_utils_parse_evr (evr1, &epoch1, &version1, &release1))
                return FALSE;