fix crash for empty measurements

Author: Dieterbe

lib/widgets/dashboard/widgets.dart

@@ -194,11 +194,12 @@ class _DashboardWeightWidgetState extends State<DashboardWeightWidget> {
                           avgs: entries7dAvg,
                         ),
                       ),
-                      MeasurementOverallChangeWidget(
-                        entries7dAvg.first,
-                        entries7dAvg.last,
-                        weightUnit(profile.isMetric, context),
-                      ),
+                      if (entries7dAvg.isNotEmpty)
+                        MeasurementOverallChangeWidget(
+                          entries7dAvg.first,
+                          entries7dAvg.last,
+                          weightUnit(profile.isMetric, context),
+                        ),
                       Row(
                         mainAxisAlignment: MainAxisAlignment.spaceBetween,
                         children: [

lib/widgets/measurements/categories_card.dart

@@ -40,11 +40,12 @@ class CategoriesCard extends StatelessWidget {
               avgs: entries7dAvg,
             ),
           ),
-          MeasurementOverallChangeWidget(
-            entries7dAvg.first,
-            entries7dAvg.last,
-            currentCategory.unit,
-          ),
+          if (entries7dAvg.isNotEmpty)
+            MeasurementOverallChangeWidget(
+              entries7dAvg.first,
+              entries7dAvg.last,
+              currentCategory.unit,
+            ),
           const Divider(),
           Row(
             mainAxisAlignment: MainAxisAlignment.spaceBetween,