Fix #4890

`strings.to_cstring` previously would not check if the buffer could
handle the extra null byte and could lead to segmentation violations
when using the resulting string in an API expecting the terminator.

core/os/os2/path_openbsd.odin

@@ -46,7 +46,7 @@ _get_executable_path :: proc(allocator: runtime.Allocator) -> (path: string, err
 		strings.write_string(&buf, "/")
 		strings.write_string(&buf, sarg)
 
-		cpath := strings.to_cstring(&buf)
+		cpath := strings.to_cstring(&buf) or_return
 		if posix.access(cpath, {.X_OK}) == .OK {
 			return real(cpath, allocator)
 		}