Fix crash occuring when searching backward in an empty list

NEWS

@@ -2,6 +2,7 @@ ncmpcpp-0.7.5 (????-??-??)
 * Action chains can be now used for seeking.
 * Fixed fetching artist info from last.fm.
 * Default value of regular_expressions was changed from 'basic' to 'perl' to work around boost issue (#12222).
+* Fixed crash occuring when searching backward in an empty list.
 
 ncmpcpp 0.7.4 (2016-04-17)
 * Fetching lyrics from lyricwiki.org was fixed.

src/helpers.h

@@ -35,6 +35,11 @@ template <typename Iterator, typename PredicateT>
 Iterator wrappedSearch(Iterator begin, Iterator current, Iterator end,
                        const PredicateT &pred, bool wrap, bool skip_current)
 {
+	if (begin == end)
+	{
+		assert(current == end);
+		return begin;
+	}
 	if (skip_current)
 		++current;
 	auto it = std::find_if(current, end, pred);