Fixes issues our internal compliance and code quality tool found:

* Adds nullptr checks and asserts to protect certain code paths
* Fixes wrong integer type in a printf call
* Adds const to const values
* Prevents integer overflow with explicit casts

code/AssetLib/FBX/FBXConverter.cpp

@@ -917,8 +917,10 @@ void FBXConverter::ConvertModel(const Model &model, aiNode *parent, aiNode *root
         } else if (line) {
             const std::vector<unsigned int> &indices = ConvertLine(*line, root_node);
             std::copy(indices.begin(), indices.end(), std::back_inserter(meshes));
-        } else {
+        } else if (geo) {
             FBXImporter::LogWarn("ignoring unrecognized geometry: ", geo->Name());
+        } else {
+            FBXImporter::LogWarn("skipping null geometry");
         }
     }
 

code/Common/DefaultIOSystem.cpp

@@ -173,7 +173,7 @@ inline static std::string MakeAbsolutePath(const char *in) {
         free(ret);
     }
 #endif
-    if (!ret) {
+    else {
         // preserve the input path, maybe someone else is able to fix
         // the path before it is accessed (e.g. our file system filter)
         ASSIMP_LOG_WARN("Invalid path: ", std::string(in));

code/Common/ScenePreprocessor.cpp

@@ -89,6 +89,9 @@ void ScenePreprocessor::ProcessScene() {
         ASSIMP_LOG_DEBUG("ScenePreprocessor: Adding default material \'" AI_DEFAULT_MATERIAL_NAME "\'");
 
         for (unsigned int i = 0; i < scene->mNumMeshes; ++i) {
+            if (nullptr == scene->mMeshes[i]) {
+                continue;
+            }
             scene->mMeshes[i]->mMaterialIndex = scene->mNumMaterials;
         }
 

code/Material/MaterialSystem.cpp

@@ -555,17 +555,23 @@ uint32_t Assimp::ComputeMaterialHash(const aiMaterial *mat, bool includeMatName
 }
 
 // ------------------------------------------------------------------------------------------------
-void aiMaterial::CopyPropertyList(aiMaterial *pcDest,
+void aiMaterial::CopyPropertyList(aiMaterial *const pcDest,
         const aiMaterial *pcSrc) {
     ai_assert(nullptr != pcDest);
     ai_assert(nullptr != pcSrc);
+    ai_assert(pcDest->mNumProperties <= pcDest->mNumAllocated);
+    ai_assert(pcSrc->mNumProperties <= pcSrc->mNumAllocated);
 
-    unsigned int iOldNum = pcDest->mNumProperties;
+    const unsigned int iOldNum = pcDest->mNumProperties;
     pcDest->mNumAllocated += pcSrc->mNumAllocated;
     pcDest->mNumProperties += pcSrc->mNumProperties;
 
+    const unsigned int numAllocated = pcDest->mNumAllocated;
     aiMaterialProperty **pcOld = pcDest->mProperties;
-    pcDest->mProperties = new aiMaterialProperty *[pcDest->mNumAllocated];
+    pcDest->mProperties = new aiMaterialProperty *[numAllocated];
+
+    ai_assert(!iOldNum || pcOld);
+    ai_assert(iOldNum < numAllocated);
 
     if (iOldNum && pcOld) {
         for (unsigned int i = 0; i < iOldNum; ++i) {

code/PostProcessing/OptimizeGraph.cpp

@@ -170,7 +170,7 @@ void OptimizeGraphProcess::CollectNewChildren(aiNode *nd, std::list<aiNode *> &n
 			++it;
 		}
 		if (join_master && !join.empty()) {
-			join_master->mName.length = ::ai_snprintf(join_master->mName.data, MAXLEN, "$MergedNode_%i", count_merged++);
+			join_master->mName.length = ::ai_snprintf(join_master->mName.data, MAXLEN, "$MergedNode_%u", count_merged++);
 
 			unsigned int out_meshes = 0;
 			for (std::list<aiNode *>::const_iterator it = join.cbegin(); it != join.cend(); ++it) {

code/PostProcessing/PretransformVertices.cpp

@@ -481,7 +481,7 @@ void PretransformVertices::Execute(aiScene *pScene) {
 			pScene->mMeshes[i]->mNumBones = 0;
 		}
 	} else {
-		apcOutMeshes.reserve(pScene->mNumMaterials << 1u);
+		apcOutMeshes.reserve(static_cast<size_t>(pScene->mNumMaterials) << 1u);
 		std::list<unsigned int> aiVFormats;
 
 		std::vector<unsigned int> s(pScene->mNumMeshes, 0);

code/PostProcessing/SortByPTypeProcess.cpp

@@ -127,7 +127,7 @@ void SortByPTypeProcess::Execute(aiScene *pScene) {
     unsigned int aiNumMeshesPerPType[4] = { 0, 0, 0, 0 };
 
     std::vector<aiMesh *> outMeshes;
-    outMeshes.reserve(pScene->mNumMeshes << 1u);
+    outMeshes.reserve(static_cast<size_t>(pScene->mNumMeshes) << 1u);
 
     bool bAnyChanges = false;