fix BSDF mixing.

Author: devshgraphicsprogramming

src/nbl/ext/MitsubaLoader/CElementBSDF.cpp

@@ -512,7 +512,7 @@ bool CElementBSDF::addProperty(SNamedPropertyElement&& _property)
 
 			if constexpr (std::is_same<state_type,MixtureBSDF>::value)
 			{
-				if (_property.type == SPropertyElementData::Type::STRING)
+				if (_property.type!=SPropertyElementData::Type::STRING)
 				{
 					error = true;
 					return;

src/nbl/ext/MitsubaLoader/CMitsubaMaterialCompilerFrontend.cpp

@@ -341,8 +341,9 @@ namespace MitsubaLoader
             auto* node = static_cast<IR::CBSDFMixNode*>(ir_node);
             const size_t cnt = _bsdf->mixturebsdf.childCount;
             ir_node->children.count = cnt;
-            for (int32_t i = cnt-1u; i >= 0; --i)
-                node->weights[i] = _bsdf->mixturebsdf.weights[i];
+            const auto* weightIt = _bsdf->mixturebsdf.weights;
+            for (int32_t i=cnt-1u; i>=0; --i) // need to add weights in reverse, because children are added using a stack
+                node->weights[i] = *(weightIt++);
         }
         break;
         }