[typescript-angular] fix: update basePath initialization

[daniel-sc]

This fixes #20760 (and was introduced in #20681).

The basePath was not correctly initialized.

@TiFu  @taxpon @sebastianhaas  @kenisteward @Vrolijkx  @macjohnny  @topce @akehir  @petejohansonxo @amakhrov @davidgamero  @mkusaka @joscha please review and/or give feedback :)

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[daniel-sc]

@TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo @amakhrov @davidgamero @mkusaka @joscha please review and/or give feedback :)

[macjohnny]

thanks for the fix!