fix: Fix low gas display label in speed-up modal

[jpuri]

Description

Fix issue that undefined is sometime visible on speedup modal. It was actually visible in edge case when 10% low is less than low estimate.

Related issues

Fixes: #28840

Manual testing steps

1. Go to test dapp
2. Submit a transaction with less gas so that it takes longer to complete
3. Open speedup modal and switch to 10% less gas estimate
4. You should not see undefined string

Screenshots/Recordings

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

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[metamaskbot]

Builds ready [56bb24d]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (MMI): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6
  • common: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9
  • content-script: 0
  • offscreen: 0
  • ui: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1807 ± 120 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	293	2778	1722	412	198
		domContentLoaded	1549	2756	1779	251	120
		load	1565	2772	1807	251	120
		domInteractive	27	81	46	18	9
		backgroundConnect	7	63	28	16	7
		firstReactRender	16	96	49	31	15
		getState	4	87	24	26	13
		initialActions	0	1	0	0	0
		loadScripts	1150	2312	1354	243	117
		setupStore	7	74	21	23	11
		uiStartup	1770	3087	2205	351	169

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 3 Bytes (0.00%)
• common: 0 Bytes (0.00%)

[metamaskbot]

Builds ready [f7102f7]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (MMI): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6
  • common: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9
  • content-script: 0
  • offscreen: 0
  • ui: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1960 ± 97 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	309	2226	1712	604	290
		domContentLoaded	1602	2206	1928	199	96
		load	1621	2212	1960	202	97
		domInteractive	26	114	54	27	13
		backgroundConnect	9	87	34	26	13
		firstReactRender	16	112	57	33	16
		getState	5	117	31	31	15
		initialActions	0	1	0	0	0
		loadScripts	1208	1678	1459	158	76
		setupStore	7	98	25	29	14
		uiStartup	1860	3049	2408	327	157

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 3 Bytes (0.00%)
• common: 0 Bytes (0.00%)