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/path-util.c

@@ -587,7 +587,7 @@ char* path_extend_internal(char **x, ...) {
 }
 
 static int check_x_access(const char *path, int *ret_fd) {
-        _cleanup_close_ int fd = -1;
+        _cleanup_close_ int fd = -EBADF;
         int r;
 
         /* We need to use O_PATH because there may be executables for which we have only exec
@@ -615,7 +615,7 @@ static int check_x_access(const char *path, int *ret_fd) {
 }
 
 static int find_executable_impl(const char *name, const char *root, char **ret_filename, int *ret_fd) {
-        _cleanup_close_ int fd = -1;
+        _cleanup_close_ int fd = -EBADF;
         _cleanup_free_ char *path_name = NULL;
         int r;