Prevent `-minus{$TableName}Row:` from catching an exception 

Prevent `-minus{$TableName}Row:` from catching an exception  when nothing was selected in a table view:  
![exception](http://i1.inmac.org/012013/56598dd92cb2a6a1.png)  

* check if there's any selected row before removing an object at this index from array  
* check if array is not empty