[Flang] Allocate character with source returns stat = 0 when already allocated

[sankeerth125]

Summary

The issue comes from the fact that AllocatableInitCharacter is called before AllocatableAllocateSource and resets the descriptor before the check is done. so made AllocatableInitCharacter called after AllocatableAllocateSource.

[clementval]

This is likely not fixing the bug. This has to be called before the actual allocation is done otherwise it has no impact.

flang/lib/Lower/Allocatable.cpp

     if (alloc.type.IsPolymorphic())
       genRuntimeAllocateApplyMold(builder, loc, box, sourceExv,
                                   alloc.getSymbol().Rank());
-    genSetDeferredLengthParameters(alloc, box);
     genAllocateObjectBounds(alloc, box);
     mlir::Value stat =
         genRuntimeAllocateSource(builder, loc, box, sourceExv, errorManager);
+    genSetDeferredLengthParameters(alloc, box);
     fir::factory::syncMutableBoxFromIRBox(builder, loc, box);
     errorManager.assignStat(builder, loc, stat);
   }