[Database] Address deadlock in player events (#2974)

* DB mutex testing

* Mutex tweaks, native string escaping

common/dbcore.h

@@ -12,6 +12,7 @@
 
 #include <mysql.h>
 #include <string.h>
+#include <mutex>
 
 class DBcore {
 public:
@@ -27,6 +28,7 @@ public:
 	void TransactionBegin();
 	void TransactionCommit();
 	void TransactionRollback();
+	std::string Escape(const std::string& s);
 	uint32 DoEscapeString(char *tobuf, const char *frombuf, uint32 fromlen);
 	void ping();
 	MYSQL *getMySQL() { return &mysql; }
@@ -57,6 +59,8 @@ private:
 	Mutex   MDatabase;
 	eStatus pStatus;
 
+	std::mutex m_query_lock{};
+
 	std::string origin_host;
 
 	char   *pHost;