Fixes issue 3855

Change-Id: I3454bf080eb581e6c49eafd773c5544ccab01434
Reviewed-on: http://gerrit.dmdirc.com/969
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>

src/com/dmdirc/addons/ui_swing/textpane/TextPaneCanvas.java

@@ -753,7 +753,7 @@ class TextPaneCanvas extends JPanel implements MouseInputListener,
                 }
             }
             LineInfo info = getClickPosition(point, true);
-            if (info.getLine() == -1 && info.getPart() == -1 && contains(point)) {
+            if (info.getLine() == -1 && info.getPart() == -1 && contains(point) && document.getNumLines() != 0) {
                 if (getFirstLineRectangle().getY() >= point.getY()) {
                     info = getFirstLineInfo();
                 } else if (getLastLineRectangle().getY() <= point.getY()) {