previous checkin broke some ASSERT statements. Fixing this problem

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403952

dlib/assert.h

@@ -89,8 +89,10 @@ namespace dlib
 
 #ifdef ENABLE_ASSERTS 
     #define DLIB_ASSERT(_exp,_message) DLIB_CASSERT(_exp,_message)
+    #define DLIB_IF_ASSERT(exp) exp
 #else
     #define DLIB_ASSERT(_exp,_message)
+    #define DLIB_IF_ASSERT(exp) 
 #endif
 
 // ----------------------------------------------------------------------------------------

dlib/matrix/matrix_utilities.h

@@ -2031,7 +2031,7 @@ namespace dlib
         >
     const matrix_op<op_add_diag<EXP> > operator+ (
         const matrix_exp<EXP>& lhs,
-        const matrix_exp<matrix_diag_op<op_identity_matrix_2<T> > >&  
+        const matrix_exp<matrix_diag_op<op_identity_matrix_2<T> > >& DLIB_IF_ASSERT(rhs)
     )
     {
         // both matrices must contain the same type of element
@@ -2062,7 +2062,7 @@ namespace dlib
         typename T
         >
     const matrix_op<op_add_diag<EXP> > operator+ (
-        const matrix_exp<matrix_diag_op<op_identity_matrix_2<T> > >& , 
+        const matrix_exp<matrix_diag_op<op_identity_matrix_2<T> > >& DLIB_IF_ASSERT(lhs), 
         const matrix_exp<EXP>& rhs
     )
     {
@@ -2279,7 +2279,7 @@ namespace dlib
         long N
         >
     const matrix_op<op_add_diag<EXP> > operator+ (
-        const matrix_exp<matrix_diag_op<op_identity_matrix<T,N> > >& , 
+        const matrix_exp<matrix_diag_op<op_identity_matrix<T,N> > >& DLIB_IF_ASSERT(lhs), 
         const matrix_exp<EXP>& rhs
     )
     {
@@ -2311,7 +2311,7 @@ namespace dlib
         >
     const matrix_op<op_add_diag<EXP> > operator+ (
         const matrix_exp<EXP>& lhs,
-        const matrix_exp<matrix_diag_op<op_identity_matrix<T,N> > >& 
+        const matrix_exp<matrix_diag_op<op_identity_matrix<T,N> > >& DLIB_IF_ASSERT(rhs)
     )
     {
         // both matrices must contain the same type of element