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/RangeTestModule.cpp

@@ -114,6 +114,8 @@ int32_t RangeTestModule::runOnce()
 void RangeTestModuleRadio::sendPayload(NodeNum dest, bool wantReplies)
 {
     meshtastic_MeshPacket *p = allocDataPacket();
+    if (!p)
+        return;
     p->to = dest;
     p->decoded.want_response = wantReplies;
     p->hop_limit = 0;