LG: Fix uninitialised and never-updated Swing(H) previous state (#2287)

* LG: Fix uninitialised and never-updated Swing(H) previous state

`updateSwingPrev()` copies `_swingv` and `_vaneswingv[]` across to their
`_prev` counterparts, but never `_swingh`. As `updateSwingPrev()` is also
what `stateReset()` uses to prime those values, `_swingh_prev` is never
initialised at all, and never updated after a send either.

That has two consequences for the AKB73757604 model, which is the only one
that consults it in `send()`:

* The first `send()` reads an uninitialised bool. UBSAN agrees:
  `ir_LG.cpp:280:24: runtime error: load of value 74, which is not a valid
  value for type 'bool'`
* The `if (_swingh != _swingh_prev)` "only send it if it changed" check
  never settles, so Swing(H) is either re-sent on every single send, or
  never sent at all -- decided by whatever was on the stack that day.

This is also why `TestIRac.LG2_AKB73757604` is flaky: it asserts six
messages get sent, and the sixth is exactly that Swing(H) message. It
passes or fails depending on that garbage value, which is a fun way to
spend an afternoon when it fails on an unrelated PR. :-)

Fixed by copying `_swingh` across in `updateSwingPrev()` like its
siblings. Added `TestIRLgAcClass.SwingHPrevIsTracked`, which fails on
master regardless of what the uninitialised value happens to be, since it
checks a repeated send doesn't re-send Swing(H).

* LG: Trim the new test's comments down to one-liners

The rationale belongs in the commit message & PR, not wrapped across four lines above the test. Matches the rest of the file, where tests carry either no comment or a single line.

Author: JayyyXp

src/ir_LG.cpp

@@ -591,6 +591,7 @@ void IRLgAc::setSwingV(const uint32_t position) {
 // Copy the previous swing settings from the current ones.
 void IRLgAc::updateSwingPrev(void) {
   _swingv_prev = _swingv;
+  _swingh_prev = _swingh;
   for (uint8_t i = 0; i < kLgAcSwingVMaxVanes; i++)
     _vaneswingv_prev[i] = _vaneswingv[i];
 }

test/ir_LG_test.cpp

@@ -1190,3 +1190,31 @@ TEST(TestIRLgAcClass, SwingVToggle) {
   EXPECT_EQ(ac._swingv, kLgAcSwingVToggle);
   EXPECT_NE(ac._swingv_prev, kLgAcSwingVToggle);
 }
+
+// Ensure Swing(H)'s previous state is initialised & kept up to date.
+TEST(TestIRLgAcClass, SwingHPrevIsTracked) {
+  IRLgAc ac(kGpioUnused);
+  ac.begin();
+  ac.setModel(lg_ac_remote_model_t::AKB73757604);
+  ac.setPower(true);
+  ac.setMode(kLgAcCool);
+  ac.setTemp(25);
+  ac.setFan(kLgAcFanLow);
+  ac.setSwingH(true);
+
+  ac._irsend.reset();
+  ac.send();
+  ac._irsend.makeDecodeResult();
+  EXPECT_EQ(121, ac._irsend.capture.rawlen);  // Normal + Swing(H) message.
+
+  ac._irsend.reset();
+  ac.send();
+  ac._irsend.makeDecodeResult();
+  EXPECT_EQ(61, ac._irsend.capture.rawlen);  // Unchanged, so normal only.
+
+  ac.setSwingH(false);
+  ac._irsend.reset();
+  ac.send();
+  ac._irsend.makeDecodeResult();
+  EXPECT_EQ(121, ac._irsend.capture.rawlen);  // Changed again, so both.
+}