pgui: Fix PGEntry::get_cursor_Y()

It returned the Y position, which is always 0.0, instead of the Z position.

Fixes #1633

panda/src/pgui/pgEntry.I

@@ -134,7 +134,6 @@ get_cursor_position() const {
 /**
  * Returns the node position x of the cursor
  */
-
 INLINE PN_stdfloat PGEntry::
 get_cursor_X() const {
   LightReMutexHolder holder(_lock);
@@ -144,14 +143,12 @@ get_cursor_X() const {
 /**
  * Returns the node position y of the cursor
  */
-
 INLINE PN_stdfloat PGEntry::
 get_cursor_Y() const {
   LightReMutexHolder holder(_lock);
-  return _cursor_def.get_y();
+  return _cursor_def.get_z();
 }
 
-
 /**
  * Sets the maximum number of characters that may be typed into the entry.
  * This is a limit on the number of characters, as opposed to the width of the