Fix session dispose bug on android

src/android/src/main/java/com/RNFetchBlob/RNFetchBlobFS.java

      * @param paths An array of file paths.
      * @param callback JS contest callback
      */
-    static void removeSession(ReadableArray paths, Callback callback) {
+    static void removeSession(ReadableArray paths, final Callback callback) {
 
         AsyncTask<ReadableArray, Integer, Integer> task = new AsyncTask<ReadableArray, Integer, Integer>() {
             @Override
             protected Integer doInBackground(ReadableArray ...paths) {
-                for(int i =0; i< paths[0].size(); i++) {
-                    File f = new File(paths[0].getString(i));
-                    if(f.exists())
-                        f.delete();
+                try {
+                    for (int i = 0; i < paths[0].size(); i++) {
+                        File f = new File(paths[0].getString(i));
+                        if (f.exists())
+                            f.delete();
+                    }
+                    callback.invoke(null, true);
+                } catch(Exception err) {
+                    callback.invoke(err.getLocalizedMessage());
                 }
                 return paths[0].size();
             }

src/class/RNFetchBlobSession.js

 const RNFetchBlob = NativeModules.RNFetchBlob
 const emitter = DeviceEventEmitter
 
+let sessions = {}
+
 export default class RNFetchBlobSession {
 
   add : (path:string) => RNFetchBlobSession;
   list : () => Array<string>;
   name : string;
 
+  static getSession(name:string):any {
+    return sessions[name]
+  }
+
+  static setSession(name:string, val:any) {
+    sessions[name] = val
+  }
+
+  static removeSession(name:string) {
+    delete sessions[name]
+  }
+
   constructor(name:string, list:Array<string>) {
     this.name = name
     if(!sessions[name]) {

src/fs.js

  * @return {RNFetchBlobSession}
  */
 function session(name:string):RNFetchBlobSession {
-  let s = sessions[name]
+  let s = RNFetchBlobSession.getSession(name)
   if(s)
     return new RNFetchBlobSession(name)
   else {
-    sessions[name] = []
+    RNFetchBlobSession.setSession(name, [])
     return new RNFetchBlobSession(name, [])
   }
 }