ttyread: test for EOF while reading tty

When a read operation returns 0 then it means that we arrived to the end of the
file, and new reads will return 0 unless you do some other operation such as
lseek(). This case happens with USB-232 adapters when they are unplugged.

st.c

@@ -823,17 +823,24 @@ ttyread(void)
 	int ret;
 
 	/* append read bytes to unprocessed bytes */
-	if ((ret = read(cmdfd, buf+buflen, LEN(buf)-buflen)) < 0)
+	ret = read(cmdfd, buf+buflen, LEN(buf)-buflen);
+
+	switch (ret) {
+	case 0:
+		fputs("Found EOF in input\n", stderr);
+		exit(0);
+	case -1:
 		die("couldn't read from shell: %s\n", strerror(errno));
+	default:
 		buflen += ret;
-
 		written = twrite(buf, buflen, 0);
 		buflen -= written;
 		/* keep any uncomplete utf8 char for the next call */
 		if (buflen > 0)
 			memmove(buf, buf + written, buflen);
-
 		return ret;
+
+	}
 }
 
 void