fix crash when max value of a serie is 0

src/axis.vala

@@ -109,16 +109,18 @@ namespace LiveChart {
                 float upper = LiveChart.cap((float) bounds.upper);
                 var divs = LiveChart.golden_divisors(upper);
 
-                float interval = upper / divs.get(0);
-                foreach(float div in divs) {
-                    interval = upper / div;
-                    if (div > 3f && div < 7f) {
-                        break;
+                if (divs.size > 0) {
+                    float interval = upper / divs.get(0);
+                    foreach(float div in divs) {
+                        interval = upper / div;
+                        if (div > 3f && div < 7f) {
+                            break;
+                        }
+                    }
+                    var limit = bounds.upper == upper ? upper : bounds.upper + interval;
+                    for (var value = 0f; value <= limit; value += interval) {
+                        ticks.values.add(value);
                     }
-                }
-                var limit = bounds.upper == upper ? upper : bounds.upper + interval;
-                for (var value = 0f; value <= limit; value += interval) {
-                    ticks.values.add(value);
                 }
             }
 

src/utils.vala

@@ -31,6 +31,11 @@ namespace LiveChart {
     }
 
     public Gee.List<float?> golden_divisors(float value) {
+        //No golden divisors for 0
+        if (value == 0) {
+            return new Gee.ArrayList<float?>();
+        }
+
         //Handle values below 1
         float factor = value < 10 ? cap(100 / value) : 1f;
         float working_value = value * factor;

tests/axis.vala

@@ -238,4 +238,13 @@ private void register_axis() {
         assert(ticks.values.get(2) == 0.8f);
         assert(ticks.values.get(3) == 1.2f);
     });
+
+    Test.add_func("/LiveChart/YAxis#get_ticks_should_not_crash_when_max_value_is_zero", () => {
+
+        var y_axis = new LiveChart.YAxis();
+        y_axis.update_bounds(0);
+
+        //when //then
+        y_axis.get_ticks();
+    });
 }

tests/chart.vala

@@ -124,4 +124,14 @@ private void register_chart() {
         });
         Gtk.main();
     });
+
+    Test.add_func("/LiveChart/Chart/#should_not_crash_if_value_added_is_zero", () => {
+        //given
+        var chart = new LiveChart.Chart();
+        var serie = new LiveChart.Serie("Test");
+        chart.add_serie(serie);
+
+        //when //then
+        chart.add_value(serie, 0);
+    });    
 }

tests/utils.vala

@@ -108,5 +108,13 @@ private void register_utils() {
         assert(divisors.get(3) == 5f);
         assert(divisors.get(4) == 2f);
         assert(divisors.get(5) == 1f);
+    });
+
+    Test.add_func("/LiveChart/Utils/golden_divisors#ShouldNotCrashWhenComputingGoldenDivisorForZero", () => {
+        //given
+        var value = 0f;
+
+        //when //then
+        LiveChart.golden_divisors(value);
     });    
 }