You should put that partition flash line after getvars.
Code:
fastboot %* getvar product 2>&1 | findstr /r /c:"^product: *MSM8974" || echo Missmatching image and device
fastboot %* getvar product 2>&1 | findstr /r /c:"^product: *MSM8974" || exit /B 1
fastboot %* getvar board_version 2>&1 | findstr /r /c:"^board_version: *4.4" && echo Missmatching board version
fastboot %* getvar board_version 2>&1 | findstr /r /c:"^board_version: *4.4" && exit /B 1
fastboot %* getvar board_version 2>&1 | findstr /r /c:"^board_version: *5.[0-9]" && echo Missmatching board version
fastboot %* getvar board_version 2>&1 | findstr /r /c:"^board_version: *5.[0-9]" && exit /B 1
fastboot %* flash partition "%~dp0images\gpt_both0.bin" || @echo "Flash partition" && exit /B 1