Fixes a bug caused by a reallocation on vector.

BUG=Database::query crashes on some situation
TEST=Manual

Review URL: https://codereview.appspot.com/6294043
Patch from Hiroshi Sumita <hsumita@chromium.org>.

src/PYDatabase.cc

@@ -46,15 +46,17 @@ class Conditions : public std::vector<std::string> {
 
     void double_ (void) {
         gint i = size ();
+        reserve (i * 2);
         do {
             push_back (at (--i));
         } while (i > 0);
     }
 
     void triple (void) {
         gint i = size ();
+        reserve (i * 3);
         do {
-            const std::string & value = std::vector<std::string>::at (--i);
+            const std::string & value = at (--i);
             push_back (value);
             push_back (value);
         } while (i > 0);