Database backends: fix bug, and small speedup

-> Redis backend: break from switch to fix bug
-> Dummy and redis backends: reserve the count so that creating the list is faster

src/database-dummy.cpp

@@ -47,6 +47,7 @@ bool Database_Dummy::deleteBlock(const v3s16 &pos)
 
 void Database_Dummy::listAllLoadableBlocks(std::vector<v3s16> &dst)
 {
+	dst.reserve(m_database.size());
 	for (std::map<s64, std::string>::const_iterator x = m_database.begin();
 			x != m_database.end(); ++x) {
 		dst.push_back(getIntegerAsBlock(x->first));