fix subscript out of range in autovector.h

[shencebebetterme]

In "autovector.h", the length of the std::vector dat_ is equal to 1+maxi_-mini_+miniloc_, therefore in the expression dat_[1+maxi_-mini_+miniloc_] the subscript definitely goes out of range.

Previously this issue causes no error because on Linux and on mac std::vector does not perform a bound check and returns whatever in the memory as the out-of-range element. The end() thus obtained still points to the correct memory, however, the above behaviour is undefined and should be avoided.

The fixes are easy.

[emstoudenmire]

Thank you for this fix - it's a welcome improvement!