Fixes issue 4009

I rewrote the code to disable and enable the buttons a while back, I'll add
this code as a fallback safety measure.

Change-Id: Ia6037f25f5222d6bf954d45f6344a0121a2dfca9
Reviewed-on: http://gerrit.dmdirc.com/1127
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>

src/com/dmdirc/addons/ui_swing/dialogs/profiles/ProfileDetailPanel.java

                 /** {@inheritDoc} */
                 @Override
                 public boolean save() {
-                    nicknames.getModel().removeElementAt(nicknames.getSelectedIndex());
+                    if (nicknames.getSelectedIndex() != -1) {
+                        nicknames.getModel().removeElementAt(nicknames.getSelectedIndex());
+                    }
                     return true;
                 }