Add GetEmbeddedTextureAndIndex() to aiScene.

It allows the caller to get the index of the embedded texture that is always computed anyway.

include/assimp/scene.h

@@ -397,22 +397,27 @@ struct aiScene
 
     //! Returns an embedded texture
     const aiTexture* GetEmbeddedTexture(const char* filename) const {
+        return GetEmbeddedTextureAndIndex(filename).first;
+    }
+
+    //! Returns an embedded texture and its index
+    std::pair<const aiTexture*, int> GetEmbeddedTextureAndIndex(const char* filename) const {
         // lookup using texture ID (if referenced like: "*1", "*2", etc.)
         if ('*' == *filename) {
             int index = std::atoi(filename + 1);
             if (0 > index || mNumTextures <= static_cast<unsigned>(index))
-                return nullptr;
-            return mTextures[index];
+                return std::make_pair(nullptr, -1);
+            return std::make_pair(mTextures[index], index);
         }
         // lookup using filename
         const char* shortFilename = GetShortFilename(filename);
         for (unsigned int i = 0; i < mNumTextures; i++) {
             const char* shortTextureFilename = GetShortFilename(mTextures[i]->mFilename.C_Str());
             if (strcmp(shortTextureFilename, shortFilename) == 0) {
-                return mTextures[i];
+                return std::make_pair(mTextures[i], i);
             }
         }
-        return nullptr;
+        return std::make_pair(nullptr, -1);
     }
 #endif // __cplusplus