fixes fetch commits and terminates exponential deepening if all commits fetched

[nikhedonia]

In some cases we mistakenly perform agit fetch origin <commithash>:<commithash> which confuses git when you try to checkout as then it does not know whether you mean the created ref or actual commit.

Furthermore we always fetch upto 13 times in our deepening algorithm before we terminate the deepening process.

This fix speeds up the process of resolving significantly.