Fix graph hangs when y <= 0

[chiahsing]

What does this implement/fix?

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes esphome/issues#5703

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx

Example entry for config.yaml:

esphome:
  name: nodemcu-32

logger:

network:

ota:

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password
  fast_connect: true

api:
  encryption:
    key: !secret api_key

esp32:
  board: esp32dev

spi:
  mosi_pin: GPIO23
  clk_pin: GPIO18

debug:
  update_interval: 5s

sensor:
  - platform: uptime
    id: uptime_sensor
    update_interval: 1s
  - platform: template
    id: template_sensor
    update_interval: 1s
    lambda: |-
      return static_cast<int>(id(uptime_sensor).state) % 16;

graph:
  - id: template_graph
    duration: 1min
    width: 100
    height: 100
    x_grid: 15s
    y_grid: 5
    min_value: 0
    max_value: 15
    traces:
      - sensor: template_sensor
        continuous: true

display:
  - platform: waveshare_epaper
    cs_pin: GPIO26
    dc_pin: GPIO27
    model: 2.13inv3
    update_interval: 1s
    lambda: |-
      it.graph(0, 0, id(template_graph));

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[probot-esphome]

Hey there @synco, mind taking a look at this pull request as it has been labeled with an integration (graph) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.45%. Comparing base (4d8b5ed) to head (3123fa2).
Report is 470 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #6593      +/-   ##
==========================================
- Coverage   53.70%   53.45%   -0.26%     
==========================================
  Files          50       50              
  Lines        9408     9543     +135     
  Branches     1654     1685      +31     
==========================================
+ Hits         5053     5101      +48     
- Misses       4056     4131      +75     
- Partials      299      311      +12     

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[chiahsing]

Fixed the test failures. PTAL