Pass shader by reference on mesh/model classes.

includes/learnopengl/mesh.h

@@ -51,7 +51,7 @@ public:
     }
 
     // render the mesh
-    void Draw(Shader shader) 
+    void Draw(Shader &shader) 
     {
         // bind appropriate textures
         unsigned int diffuseNr  = 1;

includes/learnopengl/model.h

@@ -39,7 +39,7 @@ public:
     }
 
     // draws the model, and thus all its meshes
-    void Draw(Shader shader)
+    void Draw(Shader &shader)
     {
         for(unsigned int i = 0; i < meshes.size(); i++)
             meshes[i].Draw(shader);