Fix behaviour if bad checksum detected
Fix behaviour if bad checksum detected

Problem was discovered by failing unit test:
2: FAIL: Download should fails on the first mirror (one file has a bad checksum).

Closes: #104
Approved by: ignatenkobrain

Tojaj/librepo,Tojaj/librepo,Tojaj/librepo,rpm-software-management/librepo,rpm-software-management/librepo,rpm-software-management/librepo