Fixed a bug I introduced a minute ago.

dlib/dnn/core.h

@@ -490,7 +490,7 @@ namespace dlib
 
         sstack pop(size_t num=1) 
         { 
-            DLIB_CASSERT(num < size(), "You can't pop more things from the stack than it has in it.");
+            DLIB_CASSERT(num <= size(), "You can't pop more things from the stack than it has in it.");
             return sstack(data+num, mysize-num);
         }
 

dlib/dnn/core_abstract.h

@@ -178,7 +178,7 @@ namespace dlib
         ); 
         /*!
             requires
-                - num < size()
+                - num <= size()
             ensures
                 - returns a reference to the sub-stack S such that:
                     - S.size() == size()-num.