Fix upstream issue #173 - lost UART packets.

In case the application is sending more notifications back-to-back
and the framework has no free buffer slots error code was returned
instead of false, which was interpreted as success.
Return false in such a case, in line with SD buffer overflow handling
below.

Author: Nenik

libraries/Bluefruit52Lib/src/BLECharacteristic.cpp

@@ -539,7 +539,8 @@ bool BLECharacteristic::notify(const void* data, uint16_t len)
     while ( remaining )
     {
       // TODO multiple connection support
-      if ( !Bluefruit.Gap.getHvnPacket( Bluefruit.connHandle() ) )  return NRF_ERROR_RESOURCES; //BLE_ERROR_NO_TX_PACKETS;
+      // With no free buffers, give the app a channce to retry gracefully
+      if ( !Bluefruit.Gap.getHvnPacket( Bluefruit.connHandle() ) )  return false;
 
       uint16_t packet_len = min16(max_payload, remaining);