strftime.c: set buffer length

* strftime.c (FMTV): set the buffer length before appending to
  keep just put part.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54252 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

strftime.c

@@ -326,6 +326,7 @@ rb_strftime_with_timespec(VALUE ftime, const char *format, size_t format_len,
 				const char *fmts = FMT_PADDING(fmt, def_pad); \
 				precision = FMT_PRECISION(def_prec); \
 				tmp = format_value(fmts, tmp, precision); \
+				rb_str_set_len(ftime, s-start); \
 				rb_str_append(ftime, tmp); \
 				RSTRING_GETMEM(ftime, s, len); \
 				endp = (start = s) + rb_str_capacity(ftime); \

test/ruby/test_time.rb

@@ -758,7 +758,7 @@ class TestTime < Test::Unit::TestCase
     assert_equal("-0001", t.strftime("%G"))
 
     t = Time.utc(10000000000000000000000,1,1)
-    assert_equal("10000000000000000000000", t.strftime("%Y"))
+    assert_equal("<<10000000000000000000000>>", t.strftime("<<%Y>>"))
   end
 
   def test_strftime_weeknum