[LWG #625] std::string::find_first_of() returns 0 for the empty string

The program below is expected to run succeffully to completion (since the returned value must be less than the size of the string) but instead it aborts.

$ cat t.cpp && nice gmake t && ./t
#include <cassert>
#include <string>

int main ()
{
std::string::size_type xpos =
std::string ("").find_first_of ("cba", 0, std::string::npos);

assert (std::string::npos == xpos);
}

aCC -c -I/amd/devco/sebor/dev/stdlib/include/ansi -I/usr/include -D_RWSTDDEBUG -D_RWSTD_USE_CONFIG -I/amd/devco/sebor/dev/stdlib/include -I/build/sebor/aCC-3.70-11d/include -I/amd/devco/sebor/dev/stdlib/examples/include -Aa +nostl -g +d +w +W392 +W655 +W684 +W818 +W819 +W849 t.cpp
aCC t.o -o t -Aa +nostl -Wl,+s -Wl,+vnocompatwarnings -L/build/sebor/aCC-3.70-11d/lib -L/build/sebor/aCC-3.70-11d/lib -lstd11d -lm
ABORT instruction (core dumped)