input: sdl2: Fix guest_cursor logic

Unbreaks relative mouse mode with sdl2, just like was done with sdl.c
in c3aa84b6.

Signed-off-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/ui/sdl2.c b/ui/sdl2.c
index f1532e9..e4cb9fb 100644
--- a/ui/sdl2.c
+++ b/ui/sdl2.c
@@ -403,13 +403,17 @@
         }
         qemu_input_queue_abs(scon->dcl.con, INPUT_AXIS_X, off_x + x, max_w);
         qemu_input_queue_abs(scon->dcl.con, INPUT_AXIS_Y, off_y + y, max_h);
-    } else if (guest_cursor) {
-        x -= guest_x;
-        y -= guest_y;
-        guest_x += x;
-        guest_y += y;
-        qemu_input_queue_rel(scon->dcl.con, INPUT_AXIS_X, x);
-        qemu_input_queue_rel(scon->dcl.con, INPUT_AXIS_Y, y);
+    } else {
+        if (guest_cursor) {
+            x -= guest_x;
+            y -= guest_y;
+            guest_x += x;
+            guest_y += y;
+            dx = x;
+            dy = y;
+        }
+        qemu_input_queue_rel(scon->dcl.con, INPUT_AXIS_X, dx);
+        qemu_input_queue_rel(scon->dcl.con, INPUT_AXIS_Y, dy);
     }
     qemu_input_event_sync();
 }