[ASDisplayNode Deallocation] Fix for crash when certain types are used as instance variables. (#2803)

* Fix #2802

* Change nil to NULL

Author: haritowa

AsyncDisplayKit/ASDisplayNode.mm

@@ -542,7 +542,7 @@ - (void)_scheduleIvarsForMainDeallocation
     Ivar ivar = allMyIvars[i];
     const char *type = ivar_getTypeEncoding(ivar);
 
-    if (strcmp(type, @encode(id)) == 0) {
+    if (type != NULL && strcmp(type, @encode(id)) == 0) {
       // If it's `id` we have to include it just in case.
       resultIvars[resultCount] = ivar;
       resultCount += 1;

AsyncDisplayKit/Private/ASInternalHelpers.m

@@ -107,7 +107,7 @@ BOOL ASClassRequiresMainThreadDeallocation(Class class)
 Class _Nullable ASGetClassFromType(const char *type)
 {
   // Class types all start with @"
-  if (strncmp(type, "@\"", 2) != 0) {
+  if (type == NULL || strncmp(type, "@\"", 2) != 0) {
     return nil;
   }