Fix to dynamic resize mode under change_config().

If the encoder dynamic resize is triggered and change config()
is then called, it will reset the current (resized) codec width/height
back to the the config (unresized) width/height (which will then
prevent the resizing action from occurring in encoder_loop).

Avoid this by checking for a change in the config width/height
before resetting the cm->width/height.

Change-Id: Id9d50c0ee8a943abe4b6c72bbaa02d9696f93177

vp9/encoder/vp9_encoder.c

@@ -1453,6 +1453,8 @@ static void realloc_segmentation_maps(VP9_COMP *cpi) {
 void vp9_change_config(struct VP9_COMP *cpi, const VP9EncoderConfig *oxcf) {
   VP9_COMMON *const cm = &cpi->common;
   RATE_CONTROL *const rc = &cpi->rc;
+  int last_w = cpi->oxcf.width;
+  int last_h = cpi->oxcf.height;
 
   if (cm->profile != oxcf->profile)
     cm->profile = oxcf->profile;
@@ -1505,8 +1507,10 @@ void vp9_change_config(struct VP9_COMP *cpi, const VP9EncoderConfig *oxcf) {
 
   cm->display_width = cpi->oxcf.width;
   cm->display_height = cpi->oxcf.height;
-  cm->width = cpi->oxcf.width;
-  cm->height = cpi->oxcf.height;
+  if (last_w != cpi->oxcf.width || last_h != cpi->oxcf.height) {
+    cm->width = cpi->oxcf.width;
+    cm->height = cpi->oxcf.height;
+  }
 
   if (cpi->initial_width) {
     if (cm->width > cpi->initial_width || cm->height > cpi->initial_height) {