Zero-length mChildren arrays should be nullptr (#5749)

- Children: Don't allocate a zero-length array
- aiNode::mChildren should be left nullptr instead.

code/AssetLib/3DS/3DSConverter.cpp

@@ -643,11 +643,17 @@ void Discreet3DSImporter::AddNodeToGraph(aiScene *pcSOut, aiNode *pcOut,
     }
 
     // Allocate storage for children
-    pcOut->mNumChildren = (unsigned int)pcIn->mChildren.size();
+    const unsigned int size = static_cast<unsigned int>(pcIn->mChildren.size());
+
+    pcOut->mNumChildren = size;
+    if (size == 0) {
+        return;
+    }
+
     pcOut->mChildren = new aiNode *[pcIn->mChildren.size()];
 
     // Recursively process all children
-    const unsigned int size = static_cast<unsigned int>(pcIn->mChildren.size());
+    
     for (unsigned int i = 0; i < size; ++i) {
         pcOut->mChildren[i] = new aiNode();
         pcOut->mChildren[i]->mParent = pcOut;

code/AssetLib/COB/COBLoader.cpp

@@ -372,10 +372,12 @@ aiNode *COBImporter::BuildNodes(const Node &root, const Scene &scin, aiScene *fi
     }
 
     // add children recursively
+    if (!root.temp_children.empty()) {
         nd->mChildren = new aiNode *[root.temp_children.size()]();
         for (const Node *n : root.temp_children) {
             (nd->mChildren[nd->mNumChildren++] = BuildNodes(*n, scin, fill))->mParent = nd;
         }
+    }
 
     return nd;
 }

code/AssetLib/FBX/FBXConverter.cpp

@@ -357,13 +357,13 @@ void FBXConverter::ConvertNodes(uint64_t id, aiNode *parent, aiNode *root_node)
     if (nodes.empty()) {
         parent->mNumChildren = 0;
         parent->mChildren = nullptr;
-    }
+    } else {
-
         parent->mChildren = new aiNode *[nodes.size()]();
         parent->mNumChildren = static_cast<unsigned int>(nodes.size());
         for (unsigned int i = 0; i < nodes.size(); ++i) {
             parent->mChildren[i] = nodes[i].mOwnership.release();
         }
+    }
 }
 
 void FBXConverter::ConvertLights(const Model &model, const std::string &orig_name) {

code/AssetLib/SMD/SMDLoader.cpp

@@ -400,8 +400,12 @@ void SMDImporter::AddBoneChildren(aiNode* pcNode, uint32_t iParent) {
         }
     }
 
+    // nothing to do
+    if (pcNode->mNumChildren == 0)
+        return;
+
     // now allocate the output array
-    pcNode->mChildren = new aiNode*[pcNode->mNumChildren];
+    pcNode->mChildren = new aiNode *[pcNode->mNumChildren];
 
     // and fill all subnodes
     unsigned int qq( 0 );

code/PostProcessing/ValidateDataStructure.cpp

@@ -891,6 +891,9 @@ void ValidateDSProcess::Validate(const aiNode *pNode) {
                 ReportError("aiNode \"%s\" child %i \"%s\" parent is someone else: \"%s\"", pNode->mName.C_Str(), i, pChild->mName.C_Str(), parentName);
             }
         }
+    } else if (pNode->mChildren) {
+        ReportError("aiNode::mChildren is not nullptr for empty node %s (aiNode::mNumChildren is %i)",
+                nodeName, pNode->mNumChildren);
     }
 }