Partial fix bug #1565, unit movement artifacts

Returns code for unit_mover:wait_for_anims to
invalidate hexes on unit movements. This removes
artifacts being left on screen after large animated
units have moved.

src/units/udisplay.cpp

@@ -394,6 +394,19 @@ void unit_mover::wait_for_anims()
 		animator_.wait_until(wait_until_);
 		// debug code, see unit_frame::redraw()
 		// std::cout << "   end\n";
+		/// @todo For wesnoth 1.14+: check if efficient for redrawing?
+		/// Check with large animated units too make sure artifacts are
+		/// not left on screen after unit movement in particular.
+		if ( disp_ ) { // Should always be true if we get here.
+			// Invalidate the hexes around the move that prompted this wait.
+			map_location arr[6];
+			get_adjacent_tiles(path_[current_-1], arr);
+			for ( unsigned i = 0; i < 6; ++i )
+				disp_->invalidate(arr[i]);
+			get_adjacent_tiles(path_[current_], arr);
+			for ( unsigned i = 0; i < 6; ++i )
+				disp_->invalidate(arr[i]);
+		}
 	}
 
 	// Reset data.