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/graphics/niche/InkHUD/Applets/System/Menu/MenuApplet.cpp

@@ -2614,6 +2614,8 @@ uint16_t InkHUD::MenuApplet::getSystemInfoPanelHeight()
 void InkHUD::MenuApplet::sendText(NodeNum dest, ChannelIndex channel, const char *message)
 {
     meshtastic_MeshPacket *p = router->allocForSending();
+    if (!p)
+        return;
     p->decoded.portnum = meshtastic_PortNum_TEXT_MESSAGE_APP;
     p->to = dest;
     p->channel = channel;