bugfix the check whether workspace is sufficient in the C++ interface

for sub()

src/vre2/vre2.cpp

@@ -180,7 +180,7 @@ vre2_replace(vre2 *vre2, const char * const text, const char * const rewrite,
 		*match = vre2->replace(&t, rewrite);
 		if (!*match)
 			return NULL;
-		if (t.size() > bytes + 1)
+		if (t.size() + 1 > bytes)
 			throw runtime_error("insufficient workspace");
 		*len = t.size() + 1;
 		t.copy(dest, *len);