Add unit test for empty range

CMakeLists.txt

@@ -2203,6 +2203,7 @@ if(GTEST_FOUND OR DOWNLOAD_GTEST)
     netaddr.cpp
     packer.cpp
     prng.cpp
+    sorted_array.cpp
     str.cpp
     strip_path_and_extension.cpp
     teehistorian.cpp

src/test/sorted_array.cpp

@@ -0,0 +1,9 @@
+#include <gtest/gtest.h>
+
+#include <base/tl/sorted_array.h>
+
+TEST(SortedArray, SortEmptyRange)
+{
+	sorted_array<int> x;
+	x.sort_range();
+}