fix(vgMedia): playPromise failures now remove the playPromise referen…

…ce to play can be attempted aga

playPromise attempts that are rejected drop into the catch block and were not clearing the
playPromise reference causing all subsequent attempts to play the media to fail.  The initial
if-statement checks for the existence of a playPromise and returns out if it currently exists.  This
meant that autoplay videos rejected by Safari or Chrome could not be played, even by clicking the
play button.  This change nulls out of the playPromise reference with both successful and
unsuccessful play attempts allowing future calls to play() (for example, during a click event of the
play button) the possiblity to succeed.

#724

src/core/vg-media/vg-media.ts

@@ -248,6 +248,7 @@ export class VgMedia implements OnInit, OnDestroy, IPlayable {
                     this.playPromise = null;
                 })
                 .catch(() => {
+                    this.playPromise = null;
                     // deliberately empty for the sake of eating console noise
                 });
         }