fixed issue with accelerated node iterations

Uniform values cannot be set if the shader is not bound, and calling Blit would
release the shader making subsequent iteration count updates not work. This
commit makes sure the shader is bound before trying to do so.

app/render/backend/opengl/openglworker.cpp

@@ -311,9 +311,12 @@ void OpenGLWorker::RunNodeAccelerated(const Node *node, const TimeRange &range,
 
   // Some nodes use multiple iterations for optimization
   OpenGLTextureCache::ReferencePtr output_tex;
+
   for (int iteration=0;iteration<node->AcceleratedCodeIterations();iteration++) {
     // Set iteration number
+    shader->bind();
     shader->setUniformValue("ove_iteration", iteration);
+    shader->release();
 
     // If this is not the first iteration, set the parameter that will receive the last iteration's texture
     OpenGLTextureCache::ReferencePtr source_tex = dst_refs.at((iteration+1)%dst_refs.size());