Avoided some UB warnings when trying to sort empty arrays

modules/juce_core/containers/juce_ElementComparator.h

@@ -82,12 +82,17 @@ static void sortArray (ElementComparator& comparator,
                        int lastElement,
                        const bool retainOrderOfEquivalentItems)
 {
-    SortFunctionConverter<ElementComparator> converter (comparator);
+    jassert (firstElement >= 0);
 
-    if (retainOrderOfEquivalentItems)
-        std::stable_sort (array + firstElement, array + lastElement + 1, converter);
-    else
-        std::sort        (array + firstElement, array + lastElement + 1, converter);
+    if (lastElement > firstElement)
+    {
+        SortFunctionConverter<ElementComparator> converter (comparator);
+
+        if (retainOrderOfEquivalentItems)
+            std::stable_sort (array + firstElement, array + lastElement + 1, converter);
+        else
+            std::sort        (array + firstElement, array + lastElement + 1, converter);
+    }
 }