value: Fix out-of-bound calculation
This was introduced in 2001 by 39533f43 "gstvalue: add stepped ranges"
The problem is that we could have a valid range with [0, MAXINT32]
And the resulting n1 and n2 values would be out of bound.
After reading the code, it seems as though that "+ 1" was not meant to be there.
the various checks being done with those values are:
- if (n1 != n2) # having a +1 on both doesn't change anything
- if (n1 == 0) # That would never be reached because of the +1
- if (n1 > 1) # commented as "if more than one value"