fixes a problem with miniseed files that contain traces with different seed_ids

Miniseed files get indexed for each seed_id they contain. However, during requests, after reading they are not filtered for one seed_id but all traces from the file are returned.

Example:
file contains 1 Z, N, E trace each.

Requests for the Z component return all three components in a Stream, wildcarded requests for all three components return 9 traces (3x all three components).

This is fixed here, possible influences on other file formats were not checked, though.