va{h264,h265,av1}enc: fix potential crash on devices without rate control

This fixes a crash in `gst_va_h264_enc_class_init` and `gst_va_h265_enc_class_init`
(and probably also in gst_va_av1_enc_class_init) when calling
`g_object_class_install_properties (object_class, n_props, properties);`

When rate_control_type is 0, the following code is executed in :

```
  } else {
    n_props--;
    properties[PROP_RATE_CONTROL] = NULL;
  }
```

n_props has initially a value of N_PROPERTIES but PROP_RATE_CONTROL
is not the last element in the array, so it's making
g_object_class_install_properties fail to iterate over the
properties array.

This applies the same fix to gstvah264enc.c, gstvah265enc.c and
gstvaav1enc.c.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6319>

subprojects/gst-plugins-bad/sys/va/gstvaav1enc.c

@@ -86,11 +86,11 @@ enum
   PROP_TARGET_PERCENTAGE,
   PROP_TARGET_USAGE,
   PROP_CPB_SIZE,
-  PROP_RATE_CONTROL,
   PROP_NUM_TILE_COLS,
   PROP_NUM_TILE_ROWS,
   PROP_TILE_GROUPS,
   PROP_MBBRC,
+  PROP_RATE_CONTROL,
   N_PROPERTIES
 };
 

subprojects/gst-plugins-bad/sys/va/gstvah264enc.c

@@ -100,10 +100,10 @@ enum
   PROP_BITRATE,
   PROP_TARGET_PERCENTAGE,
   PROP_TARGET_USAGE,
-  PROP_RATE_CONTROL,
   PROP_CPB_SIZE,
   PROP_AUD,
   PROP_CC,
+  PROP_RATE_CONTROL,
   N_PROPERTIES
 };
 

subprojects/gst-plugins-bad/sys/va/gstvah265enc.c

@@ -88,11 +88,11 @@ enum
   PROP_BITRATE,
   PROP_TARGET_PERCENTAGE,
   PROP_TARGET_USAGE,
-  PROP_RATE_CONTROL,
   PROP_CPB_SIZE,
   PROP_AUD,
   PROP_NUM_TILE_COLS,
   PROP_NUM_TILE_ROWS,
+  PROP_RATE_CONTROL,
   N_PROPERTIES
 };