tree-wide: use -EBADF for fd initialization

-1 was used everywhere, but -EBADF or -EBADFD started being used in various
places. Let's make things consistent in the new style.

Note that there are two candidates:
EBADF 9 Bad file descriptor
EBADFD 77 File descriptor in bad state

Since we're initializating the fd, we're just assigning a value that means
"no fd yet", so it's just a bad file descriptor, and the first errno fits
better. If instead we had a valid file descriptor that became invalid because
of some operation or state change, the other errno would fit better.

In some places, initialization is dropped if unnecessary.

src/basic/stat-util.c

@@ -65,7 +65,7 @@ int is_device_node(const char *path) {
 }
 
 int dir_is_empty_at(int dir_fd, const char *path, bool ignore_hidden_or_backup) {
-        _cleanup_close_ int fd = -1;
+        _cleanup_close_ int fd = -EBADF;
         struct dirent *buf;
         size_t m;