Fix parameters handling with implicit spec files

If no spec patterns are presented, rspec will run with empty spec list. This bug can demonstrated like this(taken from my work-related repo):
```
% rspec
....................................................................................................................................................................................................................................................................................................................

Finished in 14.48 seconds (files took 3.59 seconds to load)
308 examples, 0 failures
```
and
```
% bin/rspec --fail-fast
No examples found.


Finished in 0.0007 seconds (files took 21.11 seconds to load)
0 examples, 0 failures
```
It fails really fast indeed :smile: 
You're right, just checked `command` implementation.