string.c: consider capacity

* string.c (rb_str_resize): should consider the capacity instead
  of the old length, as pointed out by nagachika.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46413 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Conflicts:
	ChangeLog

Author: nobu

string.c

@@ -2061,7 +2061,7 @@ rb_str_resize(VALUE str, long len)
 	    if (len == slen) return str;
 	    str_make_independent_expand(str, len - slen);
 	}
-	else if (slen < len || slen - len > 1024) {
+	else if (slen < len || (RSTRING(str)->as.heap.aux.capa - len) > (len < 1024 ? len : 1024)) {
 	    REALLOC_N(RSTRING(str)->as.heap.ptr, char, len + termlen);
 	}
 	else if (len == slen) return str;