SeqFilter output might cause warning messages and further correction steps than required

[greatfireball]

I tried to correct a single sequence using proovread. During the estimation steps for masked positions I received the following errors/warnings:

Use of uninitialized value $bpN in division (/) at ../../proovread/bin/proovread line 1716, <$xgr> line 1.

Use of uninitialized value $bpN in division (/) at ../../proovread/bin/proovread line 1718, <$xgr> line 1.

Obviously, this resulted in

Masked : 0.0%
Masked < 92% total / > 3% new - continuing

Therefore, no correction step will be skipped even if everything was already masked.

Further investigation of that problem point to the SeqFilter script, which

"[..]might be ommited if to few sequences are retrieved[...]"

In my case, the N90 value was omitted and therefore, the value for masked positions is undefined.

I will provide a fix for that issue