Fix for ticket #550.

Another case where G_fatal_error has been terminating QGIS.
Also implemented suggestions in the ticket:
- only left-click will add new point/centroid
- no tool will be activated when grass edit is opened


git-svn-id: http://svn.osgeo.org/qgis/trunk@7343 c8812cc2-4d05-0410-92ff-de0c093fc19c

src/plugins/grass/qgsgrassedit.cpp

@@ -537,8 +537,6 @@ void QgsGrassEdit::init()
 
   // TODO: how to get keyboard events from canvas (shortcuts)
 
-  newPoint();
-
   restorePosition();
 
   mValid = true; 
@@ -1600,6 +1598,10 @@ void QgsGrassEdit::displayElement ( int line, const QPen & pen, int size, QPaint
 #ifdef QGISDEBUG
   std::cerr << "QgsGrassEdit::displayElement() line = " << line << std::endl;
 #endif
+
+  // is it a valid line?
+  if (line == 0)
+    return;
 
   if ( !mSymbDisplay[mLineSymb[line]] ) return;
 

src/plugins/grass/qgsgrassedittools.cpp

@@ -78,6 +78,9 @@ QgsGrassEditNewPoint::QgsGrassEditNewPoint(QgsGrassEdit* edit, bool newCentroid)
 
 void QgsGrassEditNewPoint::mouseClick(QgsPoint & point, Qt::ButtonState button)
 {
+    if ( button != Qt::LeftButton)
+      return;
+
     Vect_reset_line ( e->mEditPoints );
     e->snap ( point ); 
     Vect_append_point ( e->mEditPoints, point.x(), point.y(), 0.0 );