[evolution] Fix the compilation warning with gcc 7

[Tomas Popela <tpopela src gnome org>]

commit 419f9d5ef51e30f38e225d9d68e60a9af04910f6
Author: Tomas Popela <tpopela redhat com>
Date:   Wed Apr 12 11:04:38 2017 +0200

    Fix the compilation warning with gcc 7

 src/e-util/e-charset-combo-box.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/e-util/e-charset-combo-box.c b/src/e-util/e-charset-combo-box.c
index 1f15727..3d7c68a 100644
--- a/src/e-util/e-charset-combo-box.c
+++ b/src/e-util/e-charset-combo-box.c
@@ -154,7 +154,7 @@ charset_combo_box_run_dialog (ECharsetComboBox *combo_box)
        }
 
        charset = gtk_entry_get_text (entry);
-       g_return_if_fail (charset != NULL && charset != '\0');
+       g_return_if_fail (charset != NULL && *charset != '\0');
 
        g_object_set_data_full (
                object, "charset", g_strdup (charset),