Fix endless loop when calling scan start from scan end callback.

When attempting to connect and the scanner is running `NimBLEScan::stop` is called to stop it
which then calls the `onScanEnded` callback. If the app then starts the scan again in this
callback an endless loop will be created.

This change prevents the endless loop by setting a flag in `NimBLEDevice` that is checked before
starting a scan while a client is trying to connect.

* Adds `NimBLEDevice::setConnectionInProgress` and `NimBLEDevice::isConnectionInProgress` functions.

src/NimBLEDevice.cpp

@@ -101,6 +101,10 @@ std::vector<NimBLEAddress> NimBLEDevice::m_ignoreList{};
 std::vector<NimBLEAddress> NimBLEDevice::m_whiteList{};
 uint8_t                    NimBLEDevice::m_ownAddrType{BLE_OWN_ADDR_PUBLIC};
 
+# if defined(CONFIG_BT_NIMBLE_ROLE_CENTRAL) || defined(CONFIG_BT_NIMBLE_ROLE_PERIPHERAL)
+bool NimBLEDevice::m_connectionInProgress{false};
+# endif
+
 # ifdef ESP_PLATFORM
 #  ifdef CONFIG_BTDM_BLE_SCAN_DUPL
 uint16_t NimBLEDevice::m_scanDuplicateSize{CONFIG_BTDM_SCAN_DUPL_CACHE_SIZE};
@@ -1232,6 +1236,23 @@ bool NimBLEDevice::setCustomGapHandler(gap_event_handler handler) {
     return rc == 0;
 } // setCustomGapHandler
 
+/**
+ * @brief Set the connection in progress flag.
+ * @param [in] inProgress The connection in progress flag.
+ * @details This is used to prevent a scan from starting while a connection is in progress.
+ */
+void NimBLEDevice::setConnectionInProgress(bool inProgress) {
+    m_connectionInProgress = inProgress;
+} // setConnectionInProgress
+
+/**
+ * @brief Check if a connection is in progress.
+ * @return True if a connection is in progress.
+ */
+bool NimBLEDevice::isConnectionInProgress() {
+    return m_connectionInProgress;
+} // isConnectionInProgress
+
 /**
  * @brief Return a string representation of the address of this device.
  * @return A string representation of this device address.