Two Bugfixes for KStars

The first one was a rather profound bug. The angular distance tool was sometimes behaving weirdly. The problem boiled down to the timer updating the display and causing the SkyMap class to forget the old mouse cursor position at the point of click, thus resulting in the angular distance tool using the new point, while the user expected it to use the point where he clicked to get the popup menu. Once discovered, it was easy to swat – just replace mousePoint() with clickedPoint() in SkyMap::slotBeginAngularDistance() and SkyMap::slotEndAngularDistance() worked. More details on the kstars-devel mailing list, and me lazy and sleepy to write any more :-P.

The second one was a trivial thing where KStars was crashing because we forgot to check if a particular pointer was NULL. Put an if(m_CurrentLink == NULL) return; and it worked. See mailing list for more details, again.