RecorderThread: Open output files with O_TRUNC

The output files should generally be unique, but that's not guaranteed.
Without truncation, the output files may potentially be corrupted due to
the presence of old data at the end.

Issue: #143

Signed-off-by: Andrew Gunnerson <chillermillerlong@hotmail.com>

app/src/main/java/com/chiller3/bcr/RecorderThread.kt

@@ -172,7 +172,7 @@ class RecorderThread(
                 resultUri = outputFile.uri
 
                 try {
-                    openFile(outputFile).use {
+                    openFile(outputFile, true).use {
                         recordUntilCancelled(it)
                     }
                 } finally {
@@ -404,9 +404,11 @@ class RecorderThread(
      *
      * @throws IOException if [file] cannot be opened
      */
-    private fun openFile(file: DocumentFile): ParcelFileDescriptor =
-        context.contentResolver.openFileDescriptor(file.uri, "rw")
+    private fun openFile(file: DocumentFile, truncate: Boolean): ParcelFileDescriptor {
+        val truncParam = if (truncate) { "t" } else { "" }
+        return context.contentResolver.openFileDescriptor(file.uri, "rw$truncParam")
             ?: throw IOException("Failed to open file at ${file.uri}")
+    }
 
     /**
      * Record from [MediaRecorder.AudioSource.VOICE_CALL] until [cancel] is called or an audio