Regex: Fix reverse searching behaviour, again

src/regex_impl.cc

@@ -1195,6 +1195,12 @@ auto test_regex = UnitTest{[]{
         kak_assert(StringView{vm.captures()[0], vm.captures()[1]}  == "boz");
     }
 
+    {
+        TestVM<MatchDirection::Backward> vm{R"(foo)"};
+        kak_assert(vm.exec("foofoo", RegexExecFlags::Search));
+        kak_assert(*vm.captures()[1]  == 0);
+    }
+
     {
         TestVM<MatchDirection::Backward> vm{R"($)"};
         kak_assert(vm.exec("foo\nbar\nbaz\nqux", RegexExecFlags::Search | RegexExecFlags::NotEndOfLine));

src/selectors.cc

@@ -864,12 +864,12 @@ static bool find_prev(const Buffer& buffer, const BufferIterator& pos,
     if (pos != buffer.begin() and
         regex_search<BufferIterator, MatchDirection::Backward>(
             buffer.begin(), pos, matches, ex,
-            match_flags(buffer, buffer.begin(), pos)))
+            match_flags(buffer, buffer.begin(), pos) | RegexExecFlags::NotInitialNull))
         return true;
     wrapped = true;
     return regex_search<BufferIterator, MatchDirection::Backward>(
         buffer.begin(), buffer.end(), matches, ex,
-        match_flags(buffer, buffer.begin(), buffer.end()));
+        match_flags(buffer, buffer.begin(), buffer.end()) | RegexExecFlags::NotInitialNull);
 }
 
 template<MatchDirection direction>
@@ -881,7 +881,7 @@ Selection find_next_match(const Context& context, const Selection& sel, const Re
     wrapped = false;
     const bool found = (direction == MatchDirection::Forward) ?
         find_next(buffer, utf8::next(pos, buffer.end()), matches, regex, wrapped)
-      : find_prev(buffer, utf8::previous(pos, buffer.begin()), matches, regex, wrapped);
+      : find_prev(buffer, pos, matches, regex, wrapped);
 
     if (not found or matches[0].first == buffer.end())
         throw runtime_error(format("'{}': no matches found", regex.str()));