algo: add coalesce

I quite like this little thing even though I don't use it much anymore
(mostly because I don't use pointers much).

algorithm/include/aw/algorithm/coalesce.h

@@ -0,0 +1,18 @@
+#ifndef aw_algorithm_coalesce_h
+#define aw_algorithm_coalesce_h
+
+namespace aw {
+/*!
+ * Returns first non-null pointer, similar to
+ * the COALESCE function in SQL.
+ */
+template <typename T, typename... Ts>
+T* coalesce(T* first, Ts*... args)
+{
+	if constexpr (sizeof...(Ts) > 0)
+		return first ? first : coalesce(args...);
+	return first;
+}
+} // namespace aw
+
+#endif // aw_algorithm_coalesce_h