[ELF] - Fixed crash after incrementing end iterator.

Next code crashed under MSVS2015 for me:
this->OutSec->Info = this->Info = 1 + It - Symbols.begin();

Because It was end() and addition of 1 is not allowed. 
vector implementation catched and failed that inside:

_Myiter& operator+=(difference_type _Off)
{	// increment by integer
 #if _ITERATOR_DEBUG_LEVEL == 2
if (this->_Getcont() == 0
	|| this->_Ptr + _Off < ((_Myvec *)this->_Getcont())->_Myfirst
	|| ((_Myvec *)this->_Getcont())->_Mylast < this->_Ptr + _Off)
   {	// report error
	_DEBUG_ERROR("vector iterator + offset out of range");
	_SCL_SECURE_OUT_OF_RANGE;

llvm-svn: 292940