[Flang] Fix NULLIFY statement that returns too early for multiple procedure pointer objects. (#81164)

The current code that handles NULLIFY statement for procedure pointer
returns after the 1st object.
This PR is to remove the `return` so it can nullify multiple procedure
pointer objects.

Author: DanielCChen

flang/lib/Lower/Bridge.cpp

@@ -3115,10 +3115,10 @@ class FirConverter : public Fortran::lower::AbstractConverter {
         hlfir::Entity nullBoxProc(
             fir::factory::createNullBoxProc(*builder, loc, boxTy));
         builder->createStoreWithConvert(loc, nullBoxProc, pptr);
-        return;
+      } else {
+        fir::MutableBoxValue box = genExprMutableBox(loc, *expr);
+        fir::factory::disassociateMutableBox(*builder, loc, box);
       }
-      fir::MutableBoxValue box = genExprMutableBox(loc, *expr);
-      fir::factory::disassociateMutableBox(*builder, loc, box);
     }
   }