Make some fields in TextFile final.

Change-Id: Ib918ce2dcad368a3d8ad14aa44d3a42bf0f4cb22
Reviewed-on: http://gerrit.dmdirc.com/3508
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager

src/com/dmdirc/util/io/TextFile.java

     /**
      * The file we're dealing with.
      */
-    private Path path;
+    private final Path path;
     /**
      * The input stream we're dealing with.
      */
-    private InputStream is;
-    /**
-     * The lines we've read from the file.
-     */
-    private List<String> lines;
+    private final InputStream is;
     /**
      * The charset to use to read the file.
      */
     private final Charset charset;
+    /**
+     * The lines we've read from the file.
+     */
+    private List<String> lines;
 
     /**
      * Creates a new instance of TextFile for the specified file, and uses the
      */
     public TextFile(final Path path, final Charset charset) {
         this.path = path;
+        this.is = null;
         this.charset = charset;
     }
 
      * @since 0.6.3m1
      */
     public TextFile(final InputStream is, final Charset charset) {
+        this.path = null;
         this.is = is;
         this.charset = charset;
     }