Initialize a variable in all cases

Commit d167f9bc06 missed this one:
/src/qemu/ui/vnc-enc-tight.c:1483: warning: 'ret' may be used uninitialized in this function

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

ui/vnc-enc-tight.c

@@ -1503,6 +1503,8 @@ static int send_sub_rect_jpeg(VncState *vs, int x, int y, int w, int h,
         } else {
             ret = send_palette_rect(vs, x, y, w, h, palette);
         }
+    } else {
+        ret = 0;
     }
     return ret;
 }