std: fix StreamSource to disallow writing to a const buffer
std: fix StreamSource to disallow writing to a const buffer

zig-lang/zig,raulgrell/zig,andrewrk/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,zig-lang/zig,andrewrk/zig