UPBGE: Fix NULL returned by GetMeshMaterial.

GetMeshMaterial was based on blender material index in a previous commit. but this function is used in loop of NumMaterial() iterations.
To solve this the GetMeshMaterial was reset as original and only GetMaterialId (now renamed GetBlenderMaterialId) is still based on blender
material index.

source/gameengine/Rasterizer/RAS_MeshObject.cpp

@@ -141,6 +141,7 @@ void RAS_MeshObject::UpdateAabb()
 	unsigned int nmat = NumMaterials();
 	for (unsigned int imat = 0; imat < nmat; ++imat) {
 		RAS_MeshMaterial *mmat = GetMeshMaterial(imat);
+
 		RAS_MeshSlot *slot = mmat->m_baseslot;
 		if (!slot)
 			continue;
@@ -196,13 +197,12 @@ const STR_String& RAS_MeshObject::GetMaterialName(unsigned int matid)
 
 RAS_MeshMaterial *RAS_MeshObject::GetMeshMaterial(unsigned int matid)
 {
-	for(std::list<RAS_MeshMaterial>::iterator it = m_materials.begin();
-		it != m_materials.end();
-		++it)
-	{
-		if (it->m_index == matid) {
-			return &*it;
+	if ((m_materials.empty() == false) && (matid < m_materials.size())) {
+		list<RAS_MeshMaterial>::iterator it = m_materials.begin();
+		while (matid--) {
+			++it;
 		}
+		return &*it;
 	}
 
 	return NULL;
@@ -261,7 +261,7 @@ RAS_MeshMaterial *RAS_MeshObject::GetMeshMaterial(RAS_IPolyMaterial *mat)
 	return NULL;
 }
 
-int RAS_MeshObject::GetMaterialId(RAS_IPolyMaterial *mat)
+int RAS_MeshObject::GetBlenderMaterialId(RAS_IPolyMaterial *mat)
 {
 	list<RAS_MeshMaterial>::iterator mit;
 

source/gameengine/Rasterizer/RAS_MeshObject.h

@@ -90,7 +90,8 @@ class RAS_MeshObject
 
 	RAS_MeshMaterial *GetMeshMaterial(unsigned int matid);
 	RAS_MeshMaterial *GetMeshMaterial(RAS_IPolyMaterial *mat);
-	int GetMaterialId(RAS_IPolyMaterial *mat);
+	/// Return the material position in the mesh, like in blender.
+	int GetBlenderMaterialId(RAS_IPolyMaterial *mat);
 
 	list<RAS_MeshMaterial>::iterator GetFirstMaterial();
 	list<RAS_MeshMaterial>::iterator GetLastMaterial();

source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.cpp

@@ -836,7 +836,7 @@ void RAS_OpenGLRasterizer::DrawDerivedMesh(class RAS_MeshSlot &ms)
 	if (current_polymat->GetFlag() & RAS_BLENDERGLSL) {
 		// GetMaterialIndex return the original mface material index,
 		// increment by 1 to match what derived mesh is doing
-		current_blmat_nr = current_mesh->GetMaterialId(current_bucket->GetPolyMaterial()) + 1;
+		current_blmat_nr = current_mesh->GetBlenderMaterialId(current_bucket->GetPolyMaterial()) + 1;
 		// For GLSL we need to retrieve the GPU material attribute
 		Material* blmat = current_polymat->GetBlenderMaterial();
 		Scene* blscene = current_polymat->GetBlenderScene();
@@ -850,7 +850,7 @@ void RAS_OpenGLRasterizer::DrawDerivedMesh(class RAS_MeshSlot &ms)
 		GPU_set_material_alpha_blend(current_blend_mode);
 	} else {
 		//ms.m_pDerivedMesh->drawMappedFacesTex(ms.m_pDerivedMesh, CheckTexfaceDM, mcol);
-		current_blmat_nr = current_mesh->GetMaterialId(current_bucket->GetPolyMaterial());
+		current_blmat_nr = current_mesh->GetBlenderMaterialId(current_bucket->GetPolyMaterial());
 		current_image = current_polymat->GetBlenderImage();
 		ms.m_pDerivedMesh->drawFacesTex(ms.m_pDerivedMesh, CheckTexDM, NULL, NULL, DM_DRAW_USE_ACTIVE_UV);
 	}