fix(do_work): use implied do loop instead of vector subscript

Author: everythingfunctional

src/image_s.f90

@@ -83,10 +83,12 @@ function do_work(tasks, dag) result(tasks_left)
                 block 
                     integer, allocatable :: upstream_task_nums(:)
                     integer, allocatable :: upstream_task_imagenums(:)
+                    integer :: i
 
                     ! figure out which images have our input data
                     upstream_task_nums      = dag%dependencies_for(task_identifier)
-                    upstream_task_imagenums = task_assignment_history(upstream_task_nums)[scheduler_image]
+                    upstream_task_imagenums = &
+                        [(task_assignment_history(upstream_task_nums(i))[scheduler_image], i = 1, size(upstream_task_nums))]
 
                     ! execute task, store result
                     mailbox(task_identifier) = &