Replaced a few single-line "//" comments.

src/core/linux/SDL_fcitx.c

@@ -506,7 +506,7 @@ SDL_Fcitx_UpdateTextRect(SDL_Rect *rect)
 #endif
 
     if (cursor->x == -1 && cursor->y == -1 && cursor->w == 0 && cursor->h == 0) {
-        // move to bottom left
+        /* move to bottom left */
         int w = 0, h = 0;
         SDL_GetWindowSize(focused_win, &w, &h);
         cursor->x = 0;