a test for bad OBJ file format and code fix that handles it

code/ObjFileParser.cpp

@@ -429,13 +429,6 @@ void ObjFileParser::getFace( aiPrimitiveType type ) {
             if (type == aiPrimitiveType_POINT) {
                 ASSIMP_LOG_ERROR("Obj: Separator unexpected in point statement");
             }
-            if (iPos == 0) {
-                //if there are no texture coordinates in the file, but normals
-                if (!vt && vn) {
-                    iPos = 1;
-                    iStep++;
-                }
-            }
             iPos++;
         } else if( IsSpaceOrNewLine( *m_DataIt ) ) {
             iPos = 0;
@@ -452,6 +445,9 @@ void ObjFileParser::getFace( aiPrimitiveType type ) {
                 ++iStep;
             }
 
+            if (iPos == 1 && !vt && vn)
+                iPos = 2; // skip texture coords for normals if there are no tex coords
+
             if ( iVal > 0 ) {
                 // Store parsed index
                 if ( 0 == iPos ) {

test/unit/utObjImportExport.cpp

@@ -391,6 +391,39 @@ TEST_F(utObjImportExport, invalid_normals_uvs) {
     EXPECT_NE(nullptr, scene);
 }
 
+TEST_F(utObjImportExport, no_vt_just_vns) {
+    static const char *ObjModel =
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 0 0 0\n"
+		"v 10 0 0\n"
+		"v 0 10 0\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"vn 0 0 1\n"
+		"f 10/10 11/11 12/12\n";
+
+    Assimp::Importer myImporter;
+    const aiScene *scene = myImporter.ReadFileFromMemory(ObjModel, strlen(ObjModel), 0);
+    EXPECT_NE(nullptr, scene);
+}
+
 TEST_F( utObjImportExport, mtllib_after_g ) {
     ::Assimp::Importer importer;
     const aiScene *scene = importer.ReadFile( ASSIMP_TEST_MODELS_DIR "/OBJ/cube_mtllib_after_g.obj", aiProcess_ValidateDataStructure );