crash when searching via Tor while Fallback has been enabled

[kjozwiak]

Description

When searching via Tor with Fallback enabled, the browser will crash.

• Uploaded crash report ID: 274b0000-ff38-2d06-0000-000000000000
• Uploaded crash report ID :264b0000-ff38-2d06-0000-000000000000

Steps to Reproduce

• STR can be found via https://github.com/brave/internal/issues/766#issuecomment-823878826

Actual result:

Brave crashes when searching via Tor with Fallback enabled.

Expected result:

Brave shouldn't crash.

Reproduces how often:

100% reproducible using the above STR.

Brave version (brave://version info)

Brave | 1.25.31 Chromium: 90.0.4430.72 (Official Build) nightly (64-bit)
-- | --
Revision | b6172ef8d07ef486489a4b11b66b2eaeed50d132-refs/branch-heads/4430@{#1233}
OS | Windows 10 OS Version 2009 (Build 19042.928)

Version/Channel Information:

• Can you reproduce this issue with the current release? No
• Can you reproduce this issue with the beta channel? No
• Can you reproduce this issue with the nightly channel? Yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? N/A
• Does the issue resolve itself when disabling Brave Rewards? N/A
• Is the issue reproducible on the latest version of Chrome? N/A

Miscellaneous Information:

CCing @bbondy @SergeyZhukovsky

[btlechowski]

Verification passed on

Brave	1.23.73 Chromium: 90.0.4430.85 (Official Build) (64-bit)
Revision	5bc145d831c180d9ff94f29a0d7a2e1cbd30ef36-refs/branch-heads/4430@{#1311}
OS	Ubuntu 18.04 LTS

Verified in https://github.com/brave/internal/issues/766#issuecomment-824979063

---

Verification PASSED on macOS 11.2.3 x64 using the following build:

Brave | 1.23.73 Chromium: 90.0.4430.85 (Official Build) (x86_64)
--- | ---
Revision | 5bc145d831c180d9ff94f29a0d7a2e1cbd30ef36-refs/branch-heads/4430@{#1311}
OS | macOS Version 11.2.3 (Build 20D91)

• verification notes can be found via https://github.com/brave/internal/issues/766#issuecomment-824979063

---

Verification passed on

Brave | 1.23.73 Chromium: 90.0.4430.85 (Official Build) (64-bit)
-- | --
Revision | 5bc145d831c180d9ff94f29a0d7a2e1cbd30ef36-refs/branch-heads/4430@{#1311}
OS | Windows 10 OS Version 2004 (Build 19041.928)

• verification notes can be found via https://github.com/brave/internal/issues/766#issuecomment-824979063