Segfault - out of bounds chunk creation

[psrok1]

Values in "Create chunk" window are validated using original file bounds. After truncating file using hexedit functionality, Veles allows to set new chunk on deleted region.

If you try to save contents of that region - you'll got exception:

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc
Aborted (core dumped)