CalcTangents: zero vector is invalid for tangent/bitangent (#5432)

* CalcTangents: zero vector is invalid for tangent/bitangent

code/PostProcessing/CalcTangentsProcess.cpp

@@ -200,8 +200,10 @@ bool CalcTangentsProcess::ProcessMesh(aiMesh *pMesh, unsigned int meshIndex) {
             localBitangent.NormalizeSafe();
 
             // reconstruct tangent/bitangent according to normal and bitangent/tangent when it's infinite or NaN.
-            bool invalid_tangent = is_special_float(localTangent.x) || is_special_float(localTangent.y) || is_special_float(localTangent.z);
-            bool invalid_bitangent = is_special_float(localBitangent.x) || is_special_float(localBitangent.y) || is_special_float(localBitangent.z);
+            bool invalid_tangent = is_special_float(localTangent.x) || is_special_float(localTangent.y) || is_special_float(localTangent.z) 
+                || (-0.5f < localTangent.x && localTangent.x < 0.5f && -0.5f < localTangent.y && localTangent.y < 0.5f && -0.5f < localTangent.z && localTangent.z < 0.5f);
+            bool invalid_bitangent = is_special_float(localBitangent.x) || is_special_float(localBitangent.y) || is_special_float(localBitangent.z)
+                || (-0.5f < localBitangent.x && localBitangent.x < 0.5f && -0.5f < localBitangent.y && localBitangent.y < 0.5f && -0.5f < localBitangent.z && localBitangent.z < 0.5f);
             if (invalid_tangent != invalid_bitangent) {
                 if (invalid_tangent) {
                     localTangent = meshNorm[p] ^ localBitangent;