Fix QuickDevBar tab activation against missing pane bindings

[alexzt]

Summary

Fix ADM_QuickDevBar tab initialization on the storefront custom theme. The toolbar loads correctly in the admin theme, but on the storefront custom theme the tab markup/pane wiring can be incomplete or
mismatched, which caused tab activation to fail.

What changed

• Scope pane lookup to the same .qdb-container as the tab list.
• Skip tab groups that have no matching pane container.
• Skip individual tabs that do not have a paired pane.
• Guard toggle()/resetForTab() against missing active tabs or panes.
• Make isActiveTab() null-safe.

Why

On the storefront custom theme, the QuickDevBar tab script could fail with:

• tab is undefined
• pane is undefined

That prevented the tab content from appearing even though the active tab state changed.

On the admin theme, the same component loads normally, so this is a storefront/theme-specific markup matching issue rather than a general QuickDevBar failure.

Verification

• node --check view/base/web/js/tabbis.js