patch 8.2.2446: setting 'term' empty has different error if compiled with GUI

Problem:    Setting 'term' empty has different error if compiled with GUI.
Solution:   Insert "else". (closes #7766)
diff --git a/src/optionstr.c b/src/optionstr.c
index 8f3f0c5..c8a5b0c 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -687,7 +687,7 @@
 	if (T_NAME[0] == NUL)
 	    errmsg = N_("E529: Cannot set 'term' to empty string");
 #ifdef FEAT_GUI
-	if (gui.in_use)
+	else if (gui.in_use)
 	    errmsg = N_("E530: Cannot change term in GUI");
 	else if (term_is_gui(T_NAME))
 	    errmsg = N_("E531: Use \":gui\" to start the GUI");