Adding a custom subscription list with a nonexistent URL crashes on Android

[antonok-edm]

@tapanmodh noticed that adding a custom adblock subscription list with a random URL would cause the browser to crash, but only on Android.

Turns out #28556 is back. We're using std::vector<T>::data() without a corresponding zero-length check.

[antonok-edm]

Looks like we're missing some zero-length checks in a few other FFI functions too.

I am praying for the imminent merge of brave/brave-core#17368, but in the meantime brave/brave-core#19462 will have to do.

[kjozwiak]

Verification PASSED on Pixel 6 running Android 14 using the following build(s):

Brave | 1.57.50 Chromium: 116.0.5845.96 (Official Build) (64-bit)
--- | ---
Revision | dd68ca599736ea1ec946e2e9def70f3c705895e1
OS | Android 14; Build/UPB5.230623.003; 34; REL

Using the STR/Cases outlined via,#32301 (comment), ensured that Brave wasn't crashing when adding https://antonok.com/tmp/empty.txt into brave://adblock. Restarted Brave several times and ensured there's no crashes/issues.