Fixed formatted substring expansion [Bug #16767]

strftime.c

@@ -331,7 +331,9 @@ rb_strftime_with_timespec(VALUE ftime, const char *format, size_t format_len,
 			s += len; \
 			if (i > 0) case_conv(s, i, flags); \
 			if (precision > i) {\
+				s += i; \
 				NEEDS(precision); \
+				s -= i; \
 				memmove(s + precision - i, s, i);\
 				memset(s, padding ? padding : ' ', precision - i); \
 				s += precision;	\

test/ruby/test_time.rb

@@ -893,6 +893,13 @@ class TestTime < Test::Unit::TestCase
     assert_equal(8192, Time.now.strftime('%8192z').size)
   end
 
+  def test_strftime_wide_precision
+    t2000 = get_t2000
+    s = t2000.strftime("%28c")
+    assert_equal(28, s.size)
+    assert_equal(t2000.strftime("%c"), s.strip)
+  end
+
   def test_strfimte_zoneoffset
     t2000 = get_t2000
     t = t2000.getlocal("+09:00:00")