Warn user when input sequences were too short for a sequence analysis service

With the ability to predict on a particular region only (JAL-1391), its easy for the user to select small ranges for prediction.

Currently, Jalview doesn't raise any warnings when these predictions fail because the ranges were too small for the prediction method. Instead, there should be a warning flag shown (rather than a modal dialog) and tooltip telling the user there was a problem with predicting on that region of sequence.