streams: isNaN() in howMuchToRead() is slow #936

             6.93%
                LazyCompile:*isNaN native v8natives.js:67
                LazyCompile:*howMuchToRead _stream_readable.js:208
                LazyCompile:*Readable.read _stream_readable.js:246
                LazyCompile:*readableAddChunk _stream_readable.js:122
                LazyCompile:*onread net.js:495
                Builtin:ArgumentsAdaptorTrampoline
                Builtin:JSEntryTrampoline
                Stub:JSEntryStub
                v8::internal::Execution::Call
                v8::Function::Call
                node::AsyncWrap::MakeCallback
                node::StreamWrap::OnRead
                uv__read
                uv__stream_io
                uv__io_poll
                uv_run
                node::Start
                __libc_start_main
                0xbf4e258d4c544155