Minimal solution for infinite loop

[ThomasdenH]

This is a minimal solution to #1391.

As discussed there, the current behaviour for allocating matrices is

• Vec, Iterator or slice to Const storage:
  - If too small, panic
  - If too large, ignore remaining entries
• Vec, Iterator or slice to Dyn storage:
  - If too small, panic
  - If too large and finite, panic
  - If too large and infinite, loop indefinitely

This PR merely merges the last two cases and always panics with the same message:

• Vec, Iterator or slice to Const storage:
  - If too small, panic
  - If too large, ignore remaining entries
• Vec, Iterator or slice to Dyn storage:
  - If too small, panic
  - If too large, panic

I think it is highly unlikely that existing code relied on the infinite loop behaviour (which would most likely crash if the vec grew too big anyway), and therefore I think this can be safely merged without impacting any existing code. This leaves the decision as to what the desired behaviour would be for later.