Avoid nullptr dereference of vector_sum_col

Signed-off-by: Georgios Pinitas <georgios.pinitas@arm.com>
Change-Id: I4cc002da82da2219f3909a4e34463946cde4cf65
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/5155
Reviewed-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/core/CL/kernels/CLGEMMLowpMatrixMultiplyReshapedOnlyRHSKernel.cpp b/src/core/CL/kernels/CLGEMMLowpMatrixMultiplyReshapedOnlyRHSKernel.cpp
index eba52b0..d39900a 100644
--- a/src/core/CL/kernels/CLGEMMLowpMatrixMultiplyReshapedOnlyRHSKernel.cpp
+++ b/src/core/CL/kernels/CLGEMMLowpMatrixMultiplyReshapedOnlyRHSKernel.cpp
@@ -406,7 +406,7 @@
         kernel_name += "_fused_output_stage_fixedpoint";
         _fuse_output_stage = true;
         // If a_offset == 0, vector_sum_col can be a nullptr
-        if(a_offset != 0)
+        if(a_offset != 0 && vector_sum_col != nullptr)
         {
             build_opts.add_option("-DA_OFFSET=" + support::cpp11::to_string(a_offset));
             build_opts.add_option_if(vector_sum_col->info()->tensor_shape().num_dimensions() > 1, "-DSUM_COL_HAS_BATCHES");