Crash using Vec with not number value. (Bug #682)

Executing the following code:
cv::Vec<std::string,4> vecStr("Alice","Bob","Ted");

Make the software thrown this error:

terminate called after throwing an instance of 'std::logic_error'
what(): basic_string::_S_construct NULL not valid

because we call the constructor with a number in the default constructor: _Tp(0)

in the following line:
template<typename _Tp, int cn> inline Vec<_Tp, cn>::Vec(_Tp v0, _Tp v1, _Tp v2) {
assert(cn >= 3);
valr0 = v0; valr1 = v1; valr2 = v2;
for(int i = 3; i < cn; i++) val[i] = _Tp(0);
}

It would be better to do something like

template<typename _Tp, int cn> inline Vec<_Tp, cn>::Vec(_Tp v0, _Tp v1, _Tp v2) {
assert(cn >= 3);
valr0 = v0; valr1 = v1; valr2 = v2;
memset(&valr3,0,(&val[cn]-valr3)); //Assure the set the reserved memory to zeros
for(int i = 3; i < cn; i++) val[i] = _Tp(); //Call the default constructor
}

(Or maybe calling the default constructor let the primitive type set to zeros)