fix: select correct rows

[ESCRI11]

This closes #318

Description

The error was being originated when evaluating the following line 64bbccf#diff-7fee6935f3c7a80f87c56c1d2d61dfad16e2bc9bdce3f6530753c7e4ab0490d3R118

The error was that the sel row selector was targeting rows non existent on the R table.

This sel vector is defined here, it is basically a 1:N vector where N is selected on the righ-bar-settings, when filtering genes this R table had less than N rows so it crashed.

Now we check if N is bigger than the rows of R.

[mauromiguelm]

it works well, approved, but why is pcor_ntop giving out of bounds, when is should be a subset of rownames(R)? do we have a problem with R <- getGeneCorr() or pcor_ntop?