context: cache result of home_fd()

BeesContext::home_fd() is supposed to open $BEESHOME once and cache
the Fd for later calls; however, instead it was reopening a new Fd each
time it was called, and _also_ holding that Fd in a BeesContext member.
Fds clean themselves up when they are forgotten, so it was not leaking
per se, but it certainly had more open Fds than it needed to.

Check to see if we have m_home_fd open, and return that if so.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

src/bees-context.cc

@@ -150,6 +150,10 @@ BeesContext::show_progress()
 Fd
 BeesContext::home_fd()
 {
+	if (!!m_home_fd) {
+		return m_home_fd;
+	}
+
 	const char *base_dir = getenv("BEESHOME");
 	if (!base_dir) {
 		base_dir = ".beeshome";