Initialize characteristic array to NULL to prevent crash.

Espressif introduced a new member to the characteristic struct for the characteristic presentation format descriptor, cpfd (0x2904).
If this is not initilaized to NULL then the garbage data will be used and subsequently cause a crash on starting the server.

Author: h2zero

src/NimBLEService.cpp

@@ -159,7 +159,7 @@ bool NimBLEService::start() {
             // Nimble requires the last characteristic to have it's uuid = 0 to indicate the end
             // of the characteristics for the service. We create 1 extra and set it to null
             // for this purpose.
-            pChr_a = new ble_gatt_chr_def[numChrs + 1];
+            pChr_a = new ble_gatt_chr_def[numChrs + 1]{};
             int i = 0;
             for(auto chr_it = m_chrVec.begin(); chr_it != m_chrVec.end(); ++chr_it) {
                 if((*chr_it)->m_removed > 0) {