Fix read/write return type in rw_blocking

src/rw_blocking.cpp

@@ -15,7 +15,7 @@ int read_blocking(int fd, void *read_buf, size_t remaining)
     size_t done = 0;
     while (done < remaining)
     {
-        size_t r = read(fd, read_buf, remaining-done);
+        ssize_t r = read(fd, read_buf, remaining-done);
         if (r <= 0)
         {
             if (!errno)
@@ -41,7 +41,7 @@ int write_blocking(int fd, void *write_buf, size_t remaining)
     size_t done = 0;
     while (done < remaining)
     {
-        size_t r = write(fd, write_buf, remaining-done);
+        ssize_t r = write(fd, write_buf, remaining-done);
         if (r < 0)
         {
             if (errno != EINTR && errno != EAGAIN && errno != EPIPE)