[gnome-builder] xml-pack: quiet a Coverity error

[Sébastien Lafargue <slafargue src gnome org>]

commit e3e44147e03df88f97b21ae62c33cc659cde5fb0
Author: Sebastien Lafargue <slafargue gnome org>
Date:   Wed Jul 19 11:53:42 2017 +0200

    xml-pack: quiet a Coverity error

 plugins/xml-pack/ide-xml-rng-parser.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/plugins/xml-pack/ide-xml-rng-parser.c b/plugins/xml-pack/ide-xml-rng-parser.c
index 335fc28..aee81f5 100644
--- a/plugins/xml-pack/ide-xml-rng-parser.c
+++ b/plugins/xml-pack/ide-xml-rng-parser.c
@@ -1124,7 +1124,9 @@ parse_pattern (IdeXmlRngParser *self,
     def = ide_xml_rng_define_new (node, parent, NULL, IDE_XML_RNG_DEFINE_NOTALLOWED);
   else if (is_valid_rng_node (node, "grammar"))
     {
-      parent_grammar = self->parent_grammar;
+      if (self->grammars != NULL)
+        parent_grammar = self->parent_grammar;
+
       self->parent_grammar = old_grammar = self->grammars;
 
       grammar = parse_grammar (self, node->children);