qrexec-lib: return unsigned where only non-negative value is returned

qrexec-lib/libqrexec-utils.h

@@ -43,12 +43,12 @@ void do_fork_exec(const char *cmdline, int *pid, int *stdin_fd, int *stdout_fd,
 int peer_server_init(int port);
 char *peer_client_init(int dom, int port);
 void wait_for_vchan_or_argfd(int max, fd_set * rdset, fd_set * wrset);
-int read_ready_vchan_ext(void);
+unsigned int read_ready_vchan_ext(void);
 int read_all(int fd, void *buf, int size);
 int read_all_vchan_ext(void *buf, int size);
 int write_all(int fd, const void *buf, int size);
 int write_all_vchan_ext(const void *buf, int size);
-int buffer_space_vchan_ext(void);
+unsigned int buffer_space_vchan_ext(void);
 void fix_fds(int fdin, int fdout, int fderr);
 void set_nonblock(int fd);
 void set_block(int fd);

qrexec-lib/txrx-vchan.c

@@ -71,7 +71,7 @@ int read_all_vchan_ext(void *buf, int size)
 	return size;
 }
 
-int read_ready_vchan_ext()
+unsigned int read_ready_vchan_ext()
 {
 	int ready = libvchan_data_ready(ctrl);
 	if (ready < 0) {
@@ -81,7 +81,7 @@ int read_ready_vchan_ext()
 	return ready;
 }
 
-int buffer_space_vchan_ext()
+unsigned int buffer_space_vchan_ext()
 {
 	int space = libvchan_buffer_space(ctrl);
 	if (space < 0) {