bsp: nxp: Bound VGLite buffer reader access

[Old-Ding]

Summary\n- check the requested read limit before reading ptr[i] in bufferred_fgets()\n- guard CR/LF skipping with the available input byte count so full-buffer reads do not inspect past fd->data_buf\n\n## Verification\n- git diff --check HEAD^ HEAD -- bsp/nxp/imx/imxrt/libraries/drivers/vglite/font/buf_reader.c\n- git show --stat --check --format=fuller HEAD\n- git ls-files --eol -- bsp/nxp/imx/imxrt/libraries/drivers/vglite/font/buf_reader.c

[github-actions]

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