mtmd-cli : fix out_of_range when input image path is empty (#13244)

mtmd-cli : fix out_of_range when input image path is empty (#13244)

* fix out_of_range error  to keep the chat loop running

* Update examples/llava/mtmd-cli.cpp

Co-authored-by: Sigbjørn Skjæret <redacted>
* mtmd-cli : load image right away

* add a new line for readability

* rm printf

* Update examples/llava/mtmd-cli.cpp

Co-authored-by: Sigbjørn Skjæret <redacted>
* Update examples/llava/mtmd-cli.cpp

---------

Co-authored-by: Sigbjørn Skjæret <redacted>
Co-authored-by: Xuan Son Nguyen <redacted>
Co-authored-by: Xuan-Son Nguyen <redacted>