[gimp] libgimpbase: some minor improvements to the previous commit

[Michael Natterer <mitch src gnome org>]

commit 0ac2cf6171d0fe1fa8196cf69bdd36f61042c9cd
Author: Michael Natterer <mitch gimp org>
Date:   Thu Aug 8 13:27:04 2019 +0200

    libgimpbase: some minor improvements to the previous commit

 libgimpbase/gimpvaluearray.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/libgimpbase/gimpvaluearray.c b/libgimpbase/gimpvaluearray.c
index 5079a87e46..0df8efdc78 100644
--- a/libgimpbase/gimpvaluearray.c
+++ b/libgimpbase/gimpvaluearray.c
@@ -169,6 +169,8 @@ gimp_value_array_new_from_types (gchar **error_msg,
   GimpValueArray *value_array;
   va_list         va_args;
 
+  g_return_val_if_fail (error_msg == NULL || *error_msg == NULL, NULL);
+
   va_start (va_args, first_type);
 
   value_array = gimp_value_array_new_from_types_valist (error_msg,
@@ -182,6 +184,7 @@ gimp_value_array_new_from_types (gchar **error_msg,
 
 /**
  * gimp_value_array_new_from_types_valist:
+ * @error_msg:  return location for an error message.
  * @first_type: first type in the array, or #G_TYPE_NONE.
  * @va_args:    a va_list of GTypes and values, terminated by #G_TYPE_NONE
  *
@@ -199,11 +202,15 @@ gimp_value_array_new_from_types_valist (gchar   **error_msg,
                                         GType     first_type,
                                         va_list   va_args)
 {
-  GimpValueArray *value_array = gimp_value_array_new (0);
+  GimpValueArray *value_array;
   GType           type;
 
+  g_return_val_if_fail (error_msg == NULL || *error_msg == NULL, NULL);
+
   type = first_type;
 
+  value_array = gimp_value_array_new (type == G_TYPE_NONE ? 0 : 1);
+
   while (type != G_TYPE_NONE)
     {
       GValue value     = G_VALUE_INIT;