os: fixes for os.input(), os.get_raw_stdin(), os.get_raw_line() in case of stdin EOF

vlib/os/os.v

@@ -200,11 +200,23 @@ pub fn file_name(path string) string {
 	return path.all_after_last(path_separator)
 }
 
-// input returns a one-line string from stdin, after printing a prompt.
-pub fn input(prompt string) string {
+// input_opt returns a one-line string from stdin, after printing a prompt.
+// In the event of error (end of input), it returns `none`.
+pub fn input_opt(prompt string) ?string {
 	print(prompt)
 	flush()
-	return get_line()
+	res := get_raw_line()
+	if res.len > 0 {
+		return res.trim_right('\r\n')
+	}
+	return none
+}
+
+// input returns a one-line string from stdin, after printing a prompt.
+// In the event of error (end of input), it returns '<EOF>'.
+pub fn input(prompt string) string {
+	res := input_opt(prompt) or { return '<EOF>' }
+	return res
 }
 
 // get_line returns a one-line string from stdin
@@ -212,9 +224,8 @@ pub fn get_line() string {
 	str := get_raw_line()
 	$if windows {
 		return str.trim_right('\r\n')
-	} $else {
-		return str.trim_right('\n')
 	}
+	return str.trim_right('\n')
 }
 
 // get_lines returns an array of strings read from from stdin.