Fix video nodes material comparison.

Don't consider a material equal to another when their texture IDs
are not available yet.

Change-Id: Id4127d71abb2db33950a206dc722b24ab626e960
Task-number: QTBUG-47205
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

src/qtmultimediaquicktools/qsgvideonode_texture.cpp

@@ -138,6 +138,10 @@ public:
 
     virtual int compare(const QSGMaterial *other) const {
         const QSGVideoMaterial_Texture *m = static_cast<const QSGVideoMaterial_Texture *>(other);
+
+        if (!m_textureId)
+            return 1;
+
         int diff = m_textureId - m->m_textureId;
         if (diff)
             return diff;