null check process to avoid NPE

Author: hiteshsondhi88

FFmpegAndroid/src/main/java/com/github/hiteshsondhi88/libffmpeg/Util.java

@@ -63,6 +63,7 @@ static boolean killAsync(AsyncTask asyncTask) {
 
     static boolean isProcessCompleted(Process process) {
         try {
+            if (process == null) return true;
             process.exitValue();
             return true;
         } catch (IllegalThreadStateException e) {