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/DetectionSensorModule.cpp

@@ -131,6 +131,10 @@ void DetectionSensorModule::sendDetectionMessage()
     char *message = new char[40];
     sprintf(message, "%s detected", moduleConfig.detection_sensor.name);
     meshtastic_MeshPacket *p = allocDataPacket();
+    if (!p) {
+        delete[] message;
+        return;
+    }
     p->want_ack = false;
     p->decoded.payload.size = strlen(message);
     memcpy(p->decoded.payload.bytes, message, p->decoded.payload.size);
@@ -153,6 +157,10 @@ void DetectionSensorModule::sendCurrentStateMessage(bool state)
     char *message = new char[40];
     sprintf(message, "%s state: %i", moduleConfig.detection_sensor.name, state);
     meshtastic_MeshPacket *p = allocDataPacket();
+    if (!p) {
+        delete[] message;
+        return;
+    }
     p->want_ack = false;
     p->decoded.payload.size = strlen(message);
     memcpy(p->decoded.payload.bytes, message, p->decoded.payload.size);