bugfix for random crash when switching between presets

this is a band-aid fix for random crashes when switching between presets with multiple segments - crossfade disabled.

!! adding type initializers fixed it for me on -S3, however I still see (less frequent) crashes on esp32, due to heap corruption.

It took me hours to get a meaningful stackdump:

assert failed: heap_caps_free heap_caps.c:360 (heap != NULL && "free() target pointer is outside heap areas")

Backtrace: 0x40084ee1:0x3ffb2570 0x4008e341:0x3ffb2590 0x40094709:0x3ffb25b0 0x4008534a:0x3ffb26e0 0x40094739:0x3ffb2700 0x400e9037:0x3ffb2720 0x400e917c:0x3ffb2740 0x400eaeeb:0x3ffb2760 0x40117ec5:0x3ffb27c0 0x401184ea:0x3ffb2800 0x4013509d:0x3ffb2820

  #0  0x40084ee1:0x3ffb2570 in panic_abort at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/esp_system/panic.c:402
  #1  0x4008e341:0x3ffb2590 in esp_system_abort at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/esp_system/esp_system.c:128
  #2  0x40094709:0x3ffb25b0 in __assert_func at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/newlib/assert.c:85
  #3  0x4008534a:0x3ffb26e0 in heap_caps_free at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/heap/heap_caps.c:360
      (inlined by) heap_caps_free at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/heap/heap_caps.c:345
  #4  0x40094739:0x3ffb2700 in free at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/newlib/heap.c:39
  #5  0x400e9037:0x3ffb2720 in Segment::deallocateData() at wled00/FX_fcn.cpp:189
  #6  0x400e917c:0x3ffb2740 in Segment::resetIfRequired() at wled00/FX_fcn.cpp:206
      (inlined by) Segment::resetIfRequired() at wled00/FX_fcn.cpp:203
  #7  0x400eaeeb:0x3ffb2760 in WS2812FX::service() at wled00/FX_fcn.cpp:1216 (discriminator 2)
  #8  0x40117ec5:0x3ffb27c0 in WLED::loop() at wled00/wled.cpp:115 (discriminator 3)
  #9  0x401184ea:0x3ffb2800 in loop() at C:/src/wled00/wled00.ino:20
  #10 0x4013509d:0x3ffb2820 in loopTask(void*) at C:/Users/user/.platformio/packages/framework-arduinoespressif32/cores/esp32/main.cpp:50

ELF file SHA256: 18c20b536f4c6ef4

wled00/FX.h

@@ -395,10 +395,10 @@ typedef struct Segment {
       };
       uint16_t _aux0T;
       uint16_t _aux1T;
-      uint32_t _stepT;
-      uint32_t _callT;
-      uint8_t *_dataT;
-      uint16_t _dataLenT;
+      uint32_t _stepT = 0;
+      uint32_t _callT = 0;
+      uint8_t *_dataT = nullptr;
+      uint16_t _dataLenT = 0;
     } tmpsegd_t;
 
   private:

wled00/FX_fcn.cpp

@@ -168,6 +168,7 @@ bool Segment::allocateData(size_t len) {
   if (data && _dataLen == len) return true; //already allocated
   //DEBUG_PRINTF("--   Allocating data (%d): %p\n", len, this);
   deallocateData();
+  if (len == 0) return(false); // nothing to do
   if (Segment::getUsedSegmentData() + len > MAX_SEGMENT_DATA) {
     // not enough memory
     DEBUG_PRINTF("!!! Effect RAM depleted: %d/%d !!!\n", len, Segment::getUsedSegmentData());
@@ -184,9 +185,13 @@ bool Segment::allocateData(size_t len) {
 }
 
 void Segment::deallocateData() {
-  if (!data) return;
+  if (!data) { _dataLen = 0; return; }
   //DEBUG_PRINTF("---  Released data (%p): %d/%d -> %p\n", this, _dataLen, Segment::getUsedSegmentData(), data);
-  free(data);
+  if ((Segment::getUsedSegmentData() > 0) && (_dataLen > 0)) { // check that we don't have a dangling / inconsistent data pointer
+    free(data);
+  } else {
+    DEBUG_PRINTF("---- Released data (%p): inconsistent UsedSegmentData (%d/%d), cowardly refusing to free nothing.\n", this, _dataLen, Segment::getUsedSegmentData());
+  }
   data = nullptr;
   // WARNING it looks like we have a memory leak somewhere
   Segment::addUsedSegmentData(_dataLen <= Segment::getUsedSegmentData() ? -_dataLen : -Segment::getUsedSegmentData());
@@ -338,6 +343,7 @@ void Segment::stopTransition() {
       //DEBUG_PRINTF("--  Released duplicate data (%d): %p\n", _t->_segT._dataLenT, _t->_segT._dataT);
       free(_t->_segT._dataT);
       _t->_segT._dataT = nullptr;
+      _t->_segT._dataLenT = 0;
     }
     #endif
     delete _t;
@@ -364,6 +370,7 @@ uint16_t Segment::progress() {
 void Segment::swapSegenv(tmpsegd_t &tmpSeg) {
   if (!_t) return;
   //DEBUG_PRINTF("--  Saving temp seg: %p (%p)\n", this, tmpSeg);
+  if (nullptr == &tmpSeg) { DEBUG_PRINTLN(F("swapSegenv(): tmpSeg is nullptr !!")); return; } // sanity check
   tmpSeg._optionsT   = options;
   for (size_t i=0; i<NUM_COLORS; i++) tmpSeg._colorT[i] = colors[i];
   tmpSeg._speedT     = speed;
@@ -404,6 +411,7 @@ void Segment::swapSegenv(tmpsegd_t &tmpSeg) {
 
 void Segment::restoreSegenv(tmpsegd_t &tmpSeg) {
   //DEBUG_PRINTF("--  Restoring temp seg: %p (%p)\n", this, tmpSeg);
+  if (nullptr == &tmpSeg) {DEBUG_PRINTLN(F("restoreSegenv(): tmpSeg is nullptr !!")); return;} // sanity check
   if (_t && &(_t->_segT) != &tmpSeg) {
     // update possibly changed variables to keep old effect running correctly
     _t->_segT._aux0T = aux0;