Fix compilation error, remove extraneous block.

src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs

@@ -1993,11 +1993,9 @@ internal override IConvertibleConversion ClassifyConvertibleConversion(IOperatio
 
             Conversion result = ClassifyConversion(sourceType, destination);
 
+            if (result.IsReference && sourceConstantValue is { IsNull: true })
             {
-                if (result.IsReference && sourceConstantValue is { IsNull: true })
-                {
-                    constantValue = sourceConstantValue;
-                }
+                constantValue = sourceConstantValue;
             }
 
             return result;

src/Compilers/Core/Portable/Operations/ControlFlowGraphBuilder.cs

@@ -4505,7 +4505,7 @@ void initializeLoop()
                         _forToLoopBinaryOperatorLeftOperand = null;
                         _forToLoopBinaryOperatorRightOperand = null;
                     }
-                    else if (!operation.StepValue.GetConstantValue() != null &&
+                    else if (operation.StepValue.GetConstantValue() != null &&
                              !ITypeSymbolHelpers.IsSignedIntegralType(stepEnumUnderlyingTypeOrSelf) &&
                              !ITypeSymbolHelpers.IsUnsignedIntegralType(stepEnumUnderlyingTypeOrSelf))
                     {