some clean up

src/lib/src/shader.cpp

@@ -148,14 +148,17 @@ struct Shader::impl {
         // potentially the GL driver hasn't been loaded
         if (is_valid()) {
 
-            // deleting and detaching should happen much earlier
+            // detach first
+            for (auto s : _shader_stages) {
+                glDetachShader(_shader_program, s);
+            }
 
+            // deleting
             for (auto s : _shader_stages) {
                 glDeleteShader(s);
             }
 
             // only program needs to be deleted
-
             glDeleteProgram(_shader_program);
         }
     }