feat: support for merging LoRA weights on model conversion (#2079)

Co-authored-by: leejet <leejet714@gmail.com>

src/model_loader.cpp

@@ -115,7 +115,7 @@ void convert_tensor(void* src,
                     ggml_type dst_type,
                     int nrows,
                     int n_per_row,
-                    std::vector<float> imatrix = {}) {
+                    std::vector<float> imatrix) {
     int n = nrows * n_per_row;
     if (src_type == dst_type) {
         size_t nbytes = n * ggml_type_size(src_type) / ggml_blck_size(src_type);