Fix issue where we might leak backend processes

ethermess-backend.c

@@ -389,6 +389,8 @@ void readallx(int fd, unsigned char *buf, size_t length) {
 		ssize_t res = read(fd, &buf[completed], length - completed);
 		if (res == -1) {
 			err(1, "read");
+		} else if (res == 0) {
+			errx(1, "Unexpected EOF");
 		}
 		completed += res;
 	}