X3: Fix seek goes past the end of input

Reverts #30. Fixes #658.

include/boost/spirit/home/x3/directive/seek.hpp

@@ -28,25 +28,18 @@ namespace boost { namespace spirit { namespace x3
             Iterator& first, Iterator const& last
           , Context const& context, RContext& rcontext, Attribute& attr) const
         {
-            Iterator current(first);
-            for (/**/; current != last; ++current)
+            for (Iterator current(first);; ++current)
             {
                 if (this->subject.parse(current, last, context, rcontext, attr))
                 {
                     first = current;
                     return true;
                 }
-            }
 
-            // Test for when subjects match on input empty. Example:
-            //     comment = "//" >> seek[eol | eoi]
-            if (this->subject.parse(current, last, context, rcontext, attr))
-            {
-                first = current;
-                return true;
+                // fail only after subject fails & no input
+                if (current == last)
+                    return false;
             }
-
-            return false;
         }
     };
 

repository/test/qi/seek.cpp

@@ -97,5 +97,8 @@ int main()
         );
     }
 
+    // past the end regression GH#658
+    BOOST_TEST(!test(" ", seek['x'], space));
+
     return boost::report_errors();
 }

test/x3/seek.cpp

@@ -93,5 +93,8 @@ int main()
         BOOST_TEST(test_failure("abcdefg", x3::seek[x3::int_]));
     }
 
+    // past the end regression GH#658
+    BOOST_TEST(!test(" ", x3::seek['x'], x3::space));
+
     return boost::report_errors();
 }