[flang] Do not ICE on out-of-range data statement designator

[FruitClover]

Summary

Print error message instead of assert trigger.

flang/lib/Evaluate/fold-designator.cpp

if (std::optional<DynamicType> type{DynamicType::From(symbol)}) {
     }
   }
   return result;
 }
 
 // Reconstructs a Designator from a symbol, an offset, and a size.
 std::optional<Expr<SomeType>> OffsetToDesignator(FoldingContext &context,
     const Symbol &baseSymbol, ConstantSubscript offset, std::size_t size) {
-  CHECK(offset >= 0);
+  if (offset < 0) {
+    return std::nullopt;
+  }
   if (std::optional<DataRef> dataRef{
           OffsetToDataRef(context, NamedEntity{baseSymbol}, offset, size)}) {
     const Symbol &symbol{dataRef->GetLastSymbol()};
     if (std::optional<Expr<SomeType>> result{
             AsGenericExpr(std::move(*dataRef))}) {
       if (IsAllocatableOrPointer(symbol)) {
       } else if (auto type{DynamicType::From(symbol)}) {
         if (auto elementBytes{

flang/test/Semantics/data06.f90

subroutine s1
   !ERROR: DATA statement set has no value for 'a2(2_8)'
   data (a2(k),k=10,1,-2) / 4 * 1 /
   integer :: a3(2)
   !ERROR: DATA statement implied DO loop has a step value of zero
   data (a3(j),j=1,2,0)/2*333/
   integer :: a4(3)
   !ERROR: DATA statement designator 'a4(5_8)' is out of range
   data (a4(j),j=1,5,2) /3*222/
+  integer :: a5(3)
+  !ERROR: DATA statement designator 'a5(-2_8)' is out of range
+  data       a5(-2) / 1 /
   interface
     real function rfunc(x)
       real, intent(in) :: x
     end function
   end interface
   real, pointer :: rp
   !ERROR: Procedure 'rfunc' may not be used to initialize 'rp', which is not a procedure pointer
   data rp/rfunc/