Disable IRRMESH if IRR is disabled. Closes #1362.

Source/ThirdParty/Assimp/code/ImporterRegistry.cpp

@@ -39,6 +39,8 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 ---------------------------------------------------------------------------
 */
 
+// Modified by Lasse Oorni for Urho3D
+
 /** @file ImporterRegistry.cpp
 
 Central registry for all importers available. Do not edit this file
@@ -46,6 +48,11 @@ directly (unless you are adding new loaders), instead use the
 corresponding preprocessor flag to selectively disable formats.
 */
 
+// Urho3D: disable IRRMESH if IRR disabled
+#ifdef ASSIMP_BUILD_NO_IRR_IMPORTER
+#define ASSIMP_BUILD_NO_IRRMESH_IMPORTER
+#endif
+
 // ------------------------------------------------------------------------------------------------
 // Importers
 // (include_new_importers_here)