Made requires clause a little more sensible.

dlib/dnn/layers.h

@@ -75,10 +75,13 @@ namespace dlib
         void set_num_filters(long num) 
         {
             DLIB_CASSERT(num > 0);
+            if (num != num_filters_)
+            {
                 DLIB_CASSERT(get_layer_params().size() == 0, 
                     "You can't change the number of filters in con_ if the parameter tensor has already been allocated.");
                 num_filters_ = num;
             }
+        }
 
         double get_learning_rate_multiplier () const  { return learning_rate_multiplier; }
         double get_weight_decay_multiplier () const   { return weight_decay_multiplier; }
@@ -371,10 +374,13 @@ namespace dlib
         void set_num_filters(long num)
         {
             DLIB_CASSERT(num > 0);
+            if (num != num_filters_)
+            {
                 DLIB_CASSERT(get_layer_params().size() == 0,
                     "You can't change the number of filters in cont_ if the parameter tensor has already been allocated.");
                 num_filters_ = num;
             }
+        }
 
         double get_learning_rate_multiplier () const  { return learning_rate_multiplier; }
         double get_weight_decay_multiplier () const   { return weight_decay_multiplier; }

dlib/dnn/layers_abstract.h

@@ -730,7 +730,7 @@ namespace dlib
         /*!
             requires
                 - num > 0
-                - get_layer_params().size() == 0
+                - get_layer_params().size() == 0 || num_filters() == num
                   (i.e. You can't change the number of filters in con_ if the parameter
                   tensor has already been allocated.)
             ensures
@@ -974,7 +974,7 @@ namespace dlib
         /*!
             requires
                 - num > 0
-                - get_layer_params().size() == 0
+                - get_layer_params().size() == 0 || num_filters() == num
                   (i.e. You can't change the number of filters in cont_ if the parameter
                   tensor has already been allocated.)
             ensures