fix: update error checking for ImplicitDiscreteProblem initial conditions

Co-authored-by: vyudu <[email protected]>

Author: AayushSabharwal

src/systems/discrete_system/implicit_discrete_system.jl

@@ -298,12 +298,9 @@ function shift_u0map_forward(sys::ImplicitDiscreteSystem, u0map, defs)
     for k in collect(keys(u0map))
         v = u0map[k]
         if !((op = operation(k)) isa Shift)
-            isnothing(getunshifted(k)) &&
-                error("Initial conditions must be for the past state of the unknowns. Instead of providing the condition for $k, provide the condition for $(Shift(iv, -1)(k)).")
-
             updated[k] = v
         elseif op.steps > 0
-            error("Initial conditions must be for the past state of the unknowns. Instead of providing the condition for $k, provide the condition for $(Shift(iv, -1)(only(arguments(k)))).")
+            error("Initial conditions must be for the current or past state of the unknowns. Instead of providing the condition for $k, provide the condition for $(Shift(iv, -1)(only(arguments(k)))).")
         else
             updated[k] = v
         end