Fixed unit test in case of empty buffer #1093

Job	Run time
check_skip	5s
Find-feature	20s
build-OSW (OSW_FEATURE_STATS_STEPS, LIGHT_EDITION_V3_3, en-US)	3m 6s
build-OSW (OSW_SERVICE_EXAMPLE, LIGHT_EDITION_V3_3, en-US)	3m 9s
build-OSW (OSW_FEATURE_BLE_MEDIA_CTRL, LIGHT_EDITION_V3_3, en-US)	2m 56s
build-OSW (ANIMATION, LIGHT_EDITION_V3_3, en-US)	3m 44s
build-OSW (OSW_FEATURE_WIFI_APST\|OSW_FEATURE_WIFI, LIGHT_EDITION_V3_3, en-US)	3m 30s
build-OSW (OSW_APPS_EXAMPLES, LIGHT_EDITION_V3_3, en-US)	3m 4s
build-OSW (GPS_EDITION\|PROGMEM_TILES\|BOARD_HAS_PSRAM, LIGHT_EDITION_V3_3, en-US)	3m 58s
build-OSW (OSW_FEATURE_WIFI_ONBOOT\|OSW_FEATURE_WIFI, LIGHT_EDITION_V3_3, en-US)	3m 26s
build-OSW (OSW_FEATURE_WEATHER\|OSW_FEATURE_WIFI, LIGHT_EDITION_V3_3, en-US)	3m 15s
build-OSW (GIF_BG, LIGHT_EDITION_V3_3, en-US)	3m 50s
build-OSW (OSW_FEATURE_LUA\|LUA_C89_NUMBERS, LIGHT_EDITION_V3_3, en-US)	3m 24s
build-OSW (RAW_SCREEN_SERVER\|OSW_FEATURE_WIFI, LIGHT_EDITION_V3_3, en-US)	3m 21s
build-OSW (GPS_EDITION_ROTATED, LIGHT_EDITION_V3_3, en-US)	3m 36s
build-OSW (OSW_FEATURE_WIFI, LIGHT_EDITION_V3_3, en-US)	3m 19s
	48m 3s

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