Fixed an off by one error in an array assignment

In both stdlib_sorting_ord_sort.fypp and stdlib_sorting_sort_index.fypp there
was an off by one array assignment, that was repeated several times throough
copy/paste/edit.
                buf(0:array_len-mid) = array(mid:array_len-1)
should have been
                buf(0:array_len-mid-1) = array(mid:array_len-1)
Fixed in both files.

[ticket: X]

Author: wclodius2

src/stdlib_sorting_ord_sort.fypp

@@ -355,7 +355,7 @@ contains
                     end if
                 end do merge_lower
             else ! The right run is shorter ! check that it is stable
-                buf(0:array_len-mid) = array(mid:array_len-1)
+                buf(0:array_len-mid-1) = array(mid:array_len-1)
                 i = mid - 1
                 j = array_len - mid -1
                 merge_upper: do k = array_len-1, 0, -1
@@ -696,7 +696,7 @@ contains
                     end if
                 end do merge_lower
             else ! The right run is shorter ! check that it is stable
-                buf(0:array_len-mid) = array(mid:array_len-1)
+                buf(0:array_len-mid-1) = array(mid:array_len-1)
                 i = mid - 1
                 j = array_len - mid -1
                 merge_upper: do k = array_len-1, 0, -1
@@ -1036,7 +1036,7 @@ contains
                     end if
                 end do merge_lower
             else ! The right run is shorter ! check that it is stable
-                buf(0:array_len-mid) = array(mid:array_len-1)
+                buf(0:array_len-mid-1) = array(mid:array_len-1)
                 i = mid - 1
                 j = array_len - mid -1
                 merge_upper: do k = array_len-1, 0, -1
@@ -1373,7 +1373,7 @@ contains
                     end if
                 end do merge_lower
             else ! The right run is shorter ! check that it is stable
-                buf(0:array_len-mid) = array(mid:array_len-1)
+                buf(0:array_len-mid-1) = array(mid:array_len-1)
                 i = mid - 1
                 j = array_len - mid -1
                 merge_upper: do k = array_len-1, 0, -1

src/stdlib_sorting_sort_index.fypp

@@ -414,8 +414,8 @@ contains
                     end if
                 end do merge_lower
             else ! The right run is shorter
-                buf(0:array_len-mid) = array(mid:array_len-1)
-                ibuf(0:array_len-mid) = index(mid:array_len-1)
+                buf(0:array_len-mid-1) = array(mid:array_len-1)
+                ibuf(0:array_len-mid-1) = index(mid:array_len-1)
                 i = mid - 1
                 j = array_len - mid -1
                 merge_upper: do k = array_len-1, 0, -1
@@ -822,8 +822,8 @@ contains
                     end if
                 end do merge_lower
             else ! The right run is shorter
-                buf(0:array_len-mid) = array(mid:array_len-1)
-                ibuf(0:array_len-mid) = index(mid:array_len-1)
+                buf(0:array_len-mid-1) = array(mid:array_len-1)
+                ibuf(0:array_len-mid-1) = index(mid:array_len-1)
                 i = mid - 1
                 j = array_len - mid -1
                 merge_upper: do k = array_len-1, 0, -1
@@ -1228,8 +1228,8 @@ contains
                     end if
                 end do merge_lower
             else ! The right run is shorter
-                buf(0:array_len-mid) = array(mid:array_len-1)
-                ibuf(0:array_len-mid) = index(mid:array_len-1)
+                buf(0:array_len-mid-1) = array(mid:array_len-1)
+                ibuf(0:array_len-mid-1) = index(mid:array_len-1)
                 i = mid - 1
                 j = array_len - mid -1
                 merge_upper: do k = array_len-1, 0, -1
@@ -1631,8 +1631,8 @@ contains
                     end if
                 end do merge_lower
             else ! The right run is shorter
-                buf(0:array_len-mid) = array(mid:array_len-1)
-                ibuf(0:array_len-mid) = index(mid:array_len-1)
+                buf(0:array_len-mid-1) = array(mid:array_len-1)
+                ibuf(0:array_len-mid-1) = index(mid:array_len-1)
                 i = mid - 1
                 j = array_len - mid -1
                 merge_upper: do k = array_len-1, 0, -1