Fix RideEditor SEGV on rideselected (!)

.. When interval tree is rebuilt it can cause an issue in the
   ride editor when clearing the selection model.

.. still trying to get to the botton of a SEGV on Mac.

src/Tab.cpp

@@ -21,6 +21,7 @@
 #include "Views.h"
 #include "Athlete.h"
 #include "IntervalItem.h"
+#include "IntervalTreeView.h"
 #include "MainWindow.h"
 
 Tab::Tab(Context *context) : QWidget(context->mainWindow), context(context)
@@ -181,6 +182,10 @@ Tab::rideSelected(RideItem*)
 
     if (!context->ride) return;
 
+    // stop SEGV in widgets watching for intervals being
+    // selected whilst we are deleting them from the tree
+    context->athlete->intervalWidget->blockSignals(true);
+
     // refresh interval list for bottom left
     // first lets wipe away the existing intervals
     QList<QTreeWidgetItem *> intervals = context->athlete->allIntervals->takeChildren();
@@ -206,5 +211,7 @@ Tab::rideSelected(RideItem*)
             }
         }
     }
+    // all done, so connected widgets can receive signals now
+    context->athlete->intervalWidget->blockSignals(false);
 }