[Build Issue] Replace 0 literal with LV_PART_MAIN

[copperwall]

This fixes a build failure I'm getting when compiling the project with platfromio. LV_PART_MAIN has the same value (0x000000), but it satisfies the type issue where lv_obj_get_style_pad_top and lv_obj_get_style_pad_bottom expect their second arguments to be an lv_part_t enum. I was able to get a successful build after these changes.

Happy for any feedback!

Before

Building in release mode
Compiling .pio/build/adafruit_feather_esp32s3_reversetft/src/ui/QuestionCard.cpp.o
src/ui/QuestionCard.cpp: In member function 'void QuestionCard::startScrolling()':
src/ui/QuestionCard.cpp:167:64: error: invalid conversion from 'int' to 'lv_part_t' [-fpermissive]
  167 |     lv_coord_t pad_top    = lv_obj_get_style_pad_top   (_cont, 0);
      |                                                                ^
      |                                                                |
      |                                                                int
In file included from .pio/libdeps/adafruit_feather_esp32s3_reversetft/lvgl/src/core/lv_obj_style.h:262,
                 from .pio/libdeps/adafruit_feather_esp32s3_reversetft/lvgl/src/core/lv_obj.h:27,
                 from .pio/libdeps/adafruit_feather_esp32s3_reversetft/lvgl/lvgl.h:44,
                 from src/ui/QuestionCard.h:3,
                 from src/ui/QuestionCard.cpp:1:
.pio/libdeps/adafruit_feather_esp32s3_reversetft/lvgl/src/core/lv_obj_style_gen.h:154:80: note:   initializing argument 2 of 'int32_t lv_obj_get_style_pad_top(const lv_obj_t*, lv_part_t)'
  154 | static inline int32_t lv_obj_get_style_pad_top(const lv_obj_t * obj, lv_part_t part)
      |                                                                      ~~~~~~~~~~^~~~
src/ui/QuestionCard.cpp:168:64: error: invalid conversion from 'int' to 'lv_part_t' [-fpermissive]
  168 |     lv_coord_t pad_bottom = lv_obj_get_style_pad_bottom(_cont, 0);
      |                                                                ^
      |                                                                |
      |                                                                int
.pio/libdeps/adafruit_feather_esp32s3_reversetft/lvgl/src/core/lv_obj_style_gen.h:160:83: note:   initializing argument 2 of 'int32_t lv_obj_get_style_pad_bottom(const lv_obj_t*, lv_part_t)'
  160 | static inline int32_t lv_obj_get_style_pad_bottom(const lv_obj_t * obj, lv_part_t part)

After

Building in release mode
Compiling .pio/build/adafruit_feather_esp32s3_reversetft/src/ui/QuestionCard.cpp.o
Retrieving maximum program size .pio/build/adafruit_feather_esp32s3_reversetft/firmware.elf
Checking size .pio/build/adafruit_feather_esp32s3_reversetft/firmware.elf
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM:   [==        ]  24.8% (used 81332 bytes from 327680 bytes)
Flash: [========= ]  88.4% (used 1796194 bytes from 2031616 bytes)
Configuring upload protocol...
AVAILABLE: cmsis-dap, esp-bridge, esp-builtin, esp-prog, espota, esptool, iot-bus-jtag, jlink, minimodule, olimex-arm-usb-ocd, olimex-arm-usb-ocd-h, olimex-arm-usb-tiny-h, olimex-jtag-tiny, tumpa
CURRENT: upload_protocol = esptool
Looking for upload port...
Auto-detected: /dev/cu.Bluetooth-Incoming-Port
Forcing reset using 1200bps open/close on port /dev/cu.Bluetooth-Incoming-Port
Waiting for the new upload port...
Uploading .pio/build/adafruit_feather_esp32s3_reversetft/firmware.bin
esptool.py v4.8.9
Serial port /dev/cu.Bluetooth-Incoming-Port

[daniloc]

thank you @copperwall!