fix(29226): fix error for undefined unitInput for sending NFT

[DDDDDanica]

Description

When switching to another non-ERC721 NFT in send flow, it is possible that the input is undefined when rendered. As we didn't need to use scrollTo for this input (introduced here) , putting a conditional running is sufficient.

Related issues

Fixes: #29226

Manual testing steps

1. Go to NFT
2. Pick a non ERC721 NFT to send
3. Should not see errors in console when in the sending form

Screenshots/Recordings

Before

29226.-.NFT.Send.-.Before.mp4

After

29226.-.NFT.Send.-.After.mp4

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]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[metamaskbot]

Builds ready [6d23ac8]

• 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, 13, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1870 ± 103 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	219	2215	1704	500	240
		domContentLoaded	1478	2193	1848	210	101
		load	1492	2219	1870	215	103
		domInteractive	23	102	43	25	12
		backgroundConnect	8	70	24	17	8
		firstReactRender	15	112	49	31	15
		getState	5	71	21	21	10
		initialActions	0	1	0	0	0
		loadScripts	1094	1713	1379	178	86
		setupStore	7	79	25	23	11
		uiStartup	1724	3061	2198	313	150

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 42 Bytes (0.00%)
• common: 0 Bytes (0.00%)

[dbrans]

LGTM!