fix for stop method if song is not playing

Author: chrisweb

build/library/core.js

@@ -23,7 +23,7 @@
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"
   },
-  "version": "0.8.3",
+  "version": "0.8.4",
   "dependencies": {
     "@types/webaudioapi": "^0.0.27"
   },

package.json

@@ -733,6 +733,11 @@ export class PlayerCore {
             return;
         }
 
+        if (!sound.isPlaying) {
+            // TODO: just return or throw an error
+            return;
+        }
+
         // reset the is first time sound is being played to true
         sound.firstTimePlayed = true;