Avoid crashes in DataFilter when athlete has no activities

DataFilter evaluation requires an activity to get context,
so don't try to evaluate one when there is no current activity
to avoid crashes. It is a marginal edge case without practical
value, but better don't crash when a new user is playing around.

src/Charts/OverviewItems.cpp

@@ -1032,7 +1032,7 @@ DataOverviewItem::setData(RideItem *item)
     DataFilter parser(this, item->context, program);
 
     // so long as it evaluated correctly we can call the functions
-    if (parser.root() && parser.errorList().isEmpty()) {
+    if (parser.root() && parser.errorList().isEmpty() && parent->context->currentRideItem()) {
 
         Specification spec;
         DateRange dr;
@@ -1303,7 +1303,7 @@ DataOverviewItem::setDateRange(DateRange dr)
     DataFilter parser(this, parent->context, program);
 
     // so long as it evaluated correctly we can call the functions
-    if (parser.root() && parser.errorList().isEmpty()) {
+    if (parser.root() && parser.errorList().isEmpty() && parent->context->currentRideItem()) {
 
         Specification spec;
         spec.setDateRange(dr);

src/Core/DataFilter.cpp

@@ -3116,7 +3116,10 @@ Result DataFilter::evaluate(RideItem *item, RideFilePoint *p)
 
 Result DataFilter::evaluate(Specification spec, DateRange dr)
 {
-    if (!treeRoot || DataFiltererrors.count()) return Result(0);
+    // if there is no current ride item then there is no data
+    // so it really is ok to baulk at no current ride item here
+    // we must always have a ride since context is used
+    if (context->currentRideItem() == NULL || !treeRoot || DataFiltererrors.count()) return Result(0);
 
     Result res(0);
 
@@ -3138,11 +3141,6 @@ Result DataFilter::evaluate(Specification spec, DateRange dr)
 
 Result DataFilter::evaluate(DateRange dr, QString filter)
 {
-    // if there is no current ride item then there is no data
-    // so it really is ok to baulk at no current ride item here
-    // we must always have a ride since context is used
-    if (context->currentRideItem() == NULL || !treeRoot || DataFiltererrors.count()) return Result(0);
-
     // reset stack
     rt.stack = 0;