Add check that Position is set in panIntoView()

* If panIntoView is an API method, it may now be called when the
   position of the overlay has not yet been set.

 * Adds a check for a set position to the panIntoView() method,
   and removes the now unneccessary check in handlePositionChanged()

src/ol/Overlay.js

@@ -328,9 +328,7 @@ class Overlay extends BaseObject {
    */
   handlePositionChanged() {
     this.updatePixelPosition();
-    if (this.get(Property.POSITION) && this.autoPan) {
+    this.performAutoPan();
-      this.performAutoPan();
-    }
   }
 
   /**
@@ -403,7 +401,7 @@ class Overlay extends BaseObject {
   panIntoView(panIntoViewOptions) {
     const map = this.getMap();
 
-    if (!map || !map.getTargetElement()) {
+    if (!map || !map.getTargetElement() || !this.get(Property.POSITION)) {
       return;
     }