mtmd : resize Gemma 4 images without letterbox padding (#30922)

* mtmd : resize Gemma 4 images without letterbox padding

* Apply suggestion from @ngxson

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Co-authored-by: Xuan-Son Nguyen <thichthat@gmail.com>

tools/mtmd/clip.cpp

@@ -1842,6 +1842,7 @@ struct clip_model_loader {
                         log_ffn_op = "gelu";
                         hparams.n_merge = 3; // pooling_kernel_size
                         hparams.image_resize_algo = RESIZE_ALGO_BICUBIC;
+                        hparams.image_resize_pad  = PAD_NONE;
                         get_u32(KEY_PROJ_SCALE_FACTOR, hparams.n_merge, false);
                         if (model.proj_type == PROJECTOR_TYPE_GEMMA4UV) {
                             // for "unified" variant, we directly use a bigger patch size, because the "token merging" is done directly on conv layer