app_stack: Include current location if branch fails

Previously, the error emitted when app_stack tries
to branch to a dialplan location that doesn't exist
has included only the information about the attempted
branch in the error log. This adds the current location
as well so users can see where the branch failed in
the logs.

ASTERISK-29626

Change-Id: Ia23502ab2ad21485a1ac74295063a8f25a6df5ce