add checks

Author: jvdp1

src/stdlib_selection.fypp

@@ -86,6 +86,7 @@ contains
           if(present(right)) r = right
 
           if(k < 1_ip .or. k > size(a, kind=ip) .or. l > r .or. l < 1_ip .or. &
+              k < l .or. k > r .or.      &             !i.e. if k is not in the interval [l; r]  
               r > size(a, kind=ip)) then
               error stop "select must have 1 <= k <= size(a), and 1 <= left <= right <= size(a)";
           end if
@@ -202,6 +203,7 @@ contains
           end if
 
           if(k < 1_ip .or. k > size(a, kind=ip) .or. l > r .or. l < 1_ip .or. &
+              k < l .or. k > r .or.      &             !i.e. if k is not in the interval [l; r]  
               r > size(a, kind=ip)) then
               error stop "arg_select must have 1 <= k <= size(a), and 1 <= left <= right <= size(a)";
           end if