Fix loader to avoid crashing on old shaders

src/Materials/Node/nodeMaterial.ts

@@ -1720,6 +1720,10 @@ export class NodeMaterial extends PushMaterial {
             for (var candidate of source.blocks) {
                 let target = map[candidate.id];
 
+                if (!target) {
+                    continue;
+                }
+
                 for (var input of candidate.inputs) {
                     if (map[input.targetBlockId] === block && input.targetConnectionName === outputPoint.name) {
                         let inputPoint = target.getInputByName(input.inputName);
@@ -1766,6 +1770,10 @@ export class NodeMaterial extends PushMaterial {
             let parsedBlock = source.blocks[blockIndex];
             let block = map[parsedBlock.id];
 
+            if (!block) {
+                continue;
+            }
+
             if (block.inputs.length && !merge) {
                 continue;
             }