omit progress calls on half steps to avoid oscillation

The progress call on each half step would increase the time
without increasing the step count, making the average go up;
it would then go down again on the whole step update.

Author: wbruna

stable-diffusion.cpp

@@ -1274,7 +1274,7 @@ class StableDiffusionGGML {
             }
 
             int64_t t1 = ggml_time_us();
-            if (step != 0) {
+            if (step > 0 || step == -(int)steps) {
                 int showstep = std::abs(step);
                 pretty_progress(showstep, (int)steps, (t1 - t0) / 1000000.f / showstep);
                 // LOG_INFO("step %d sampling completed taking %.2fs", step, (t1 - t0) * 1.0f / 1000000);