fix tests on index array

Author: jvdp1

src/stdlib_sorting_sort_index.fypp

@@ -106,18 +106,18 @@ contains
         ${t2}$, allocatable :: buf(:)
         ${ti}$, allocatable :: ibuf(:)
 
-        if ( size(array, kind=int_index) > huge(1_${ki}$) then
+        array_size = size(array, kind=int_index)
+
+        if ( array_size > huge(index)) then
             error stop "Too many entries for the kind of index."
         end if
 
-        array_size = size(array, kind=int_index)
-
-        if ( size(index, kind=int_index) < array_size ) then
-            error stop "index array is too small."
+        if ( array_size > size(index, kind=int_index) ) then
+            error stop "Too many entries for the size of index."
         end if
 
         do i = 0, array_size-1
-            index(i) = i+1
+            index(i) = int(i+1, kind=${ki}$)
         end do
 
         if ( optval(reverse, .false.) ) then