Null-check packet allocations in allocForSending and its callers (#11086)

* Null-check packet allocations in allocForSending and its callers

Sibling of 0ae44d701.

* Null-check allocDataProtobuf, allocAckNak and allocErrorResponse callers

Second tier of the same nullable contract.

* Keep telemetry sleep scheduling on allocation failure

Allocation failure now marks the telemetry invalid instead of returning
early, so power-saving SENSOR nodes still arm deep sleep.

src/modules/games/GamesModule.cpp

@@ -105,6 +105,8 @@ void GamesModule::announceHighScore(const char *initials, uint32_t score)
     if (!initials || initials[0] == '\0')
         return;
     meshtastic_MeshPacket *p = allocDataPacket();
+    if (!p)
+        return;
     p->to = NODENUM_BROADCAST;
     p->channel = 0; // primary channel
     p->decoded.portnum = meshtastic_PortNum_TEXT_MESSAGE_APP;