AOM encoder: default number of threads should not exceed maximum (#1221)

libheif/plugins/encoder_aom.cc

@@ -238,16 +238,17 @@ static void aom_init_parameters()
   p->version = 2;
   p->name = kParam_threads;
   p->type = heif_encoder_parameter_type_integer;
-  unsigned int threads = std::thread::hardware_concurrency();
+  p->has_default = true;
+  p->integer.have_minimum_maximum = true;
+  p->integer.minimum = 1;
+  p->integer.maximum = 64;
+  int threads = static_cast<int>(std::thread::hardware_concurrency());
   if (threads == 0) {
     // Could not autodetect, use previous default value.
     threads = 4;
   }
+  threads = std::min(threads, p->integer.maximum);
   p->integer.default_value = threads;
-  p->has_default = true;
-  p->integer.have_minimum_maximum = true;
-  p->integer.minimum = 1;
-  p->integer.maximum = 64;
   p->integer.valid_values = NULL;
   p->integer.num_valid_values = 0;
   d[i++] = p++;